Fixes ArcticaProject/nx-libs#516.

debian/control: All Priority: extras packages are required to be changed to Priority: optional by recent Debian Policy.

Attributes GH PR #591: https://github.com/ArcticaProject/nx-libs/pull/591

nxagentInitKeyboardState -> nxagentInitXkbKeyboardState
nxagentHandleKeyboardEvent -> nxagentHandleXkbKeyboardStateEvent

If xorg upstream xkb gets extended one day the previous code would not
block new xkb calls even if they would change keyboard settings. So
only act on the currently known calls and throw an error for all
unknown calls.

Fixes ArcticaProject/nx-libs#257

This helps understanding the intention of the following code.

Attributes GH PR #602: https://github.com/ArcticaProject/nx-libs/pull/602

this ensures that randr updates its private structures

If -rrxinerama was specified xrandr handling was broken. Adding/using
a custom resolution via xrandr was not working anymore.

Fixes: ArcticaProject/nx-libs#596

Attributes GH PR #594: https://github.com/ArcticaProject/nx-libs/pull/594

Fixes ArcticaProject/nx-libs#530

Fixes this:

CXX      Loop.lo
Loop.cpp: In function 'void handleCheckResultInLoop(int&, int&, int&, fd_set&, fd_set&, timeval&, timeval&)':
Loop.cpp:14080:68: warning: declaration of 'startTs' shadows a global declaration [-Wshadow]
                                             struct timeval &startTs)
                                                                    ^
Loop.cpp:1020:13: note: shadowed declaration is here
T_timestamp startTs;

Fixes ArcticaProject/nx-libs#545

Attributes GH PR #595: https://github.com/ArcticaProject/nx-libs/pull/595

Code was here twice and could be simply merged.

Attributes GH PR #597: https://github.com/ArcticaProject/nx-libs/pull/597

Reviewed+approved by Mihai Moldovan (via IRC): 2017-12-11:

```
  09:38 < Ionic> okay
  09:38 < Ionic> in that case it's probably really best to drop it completely
```

Xserver/os/xprintf.c: Drop NoMachine's own implementation of Xvasprintf(). Use stock implementation instead.

 * Reason from NoMachine's NX CHANGELOG for having its own implementation
   of Xvasprintf() (from around nxagent 3.3.0):

    - Fixed TR06G02225. The implementation of Xvprintf() has been reviewed
      to work on more platforms. Previous implementation caused a failure
      in the build of keyboard map on some platform like Solaris 8 and 9.
    - Fixed TR03G02198. Reimplemented Xvprintf() in Xserver/os to handle
      the case in which vsnprintf returned -1.

 * Reason for removing it again:

    - Fixes segfaults in SetDefaultFontPath when launching nxagent.
    - All locations in Xserver/** using the code check for return value
      of -1.
    - Solaris 8 and 9 are beyond of our support scope.
    - Keep more in sync with X.org.
    - Good moment to drop more GPL-2 code from Xserver's code base.

nx-X11/programs/Xserver/os/xprintf.c: remove doubly-defined Xscnprintf function, add missing header includes.

Fix up for 1e3a9748, which has been
faulty in this regard.

Attributes GH PR #592: https://github.com/ArcticaProject/nx-libs/pull/592

Backported from X.org:

commit 5c2e2a164d615ab06be28a663734e782614b5cc7
Author: Daniel Kurtz <djkurtz@chromium.org>
Date:   Wed Apr 18 09:51:51 2012 +0000

    os/xprintf: add Xvscnprintf and Xscnprintf

    Normal snprintf() usually returns the number of bytes that would have been
    written into a buffer had the buffer been long enough.

    The scnprintf() variants return the actual number of bytes written,
    excluding the trailing '\0'.
Signed-off-by: Daniel Kurtz <djkurtz@chromium.org>
Reviewed-by: Peter Hutterer <peter.hutterer@who-t.net>
Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
Backported-to-NX-by: Mihai Moldovan <ionic@ionic.de>

Backported from X.org:

commit 1324b0ca9f8a7fdaf03b374c75eb3c9df407c2f1
Author: Colin Harrison <colin.harrison@virgin.net>
Date:   Fri Dec 10 00:08:24 2010 +0000

    Typo in xserver Xvasprintf()

    I needed this patch in the wrapper around vsnprintf() in os/xprintf.c
    (MinGW for Windows build) to correct various crashes.
Reviewed-by: Alan Coopersmith <alan.coopersmith@oracle.com>
Backported-to-NX-by: Mihai Moldovan <ionic@ionic.de>

Backported from X.org:

commit c95c1d338fdb62dbe3dba934b97324fa778b7fce
Author: Alan Coopersmith <alan.coopersmith@oracle.com>
Date:   Sat Nov 27 18:43:12 2010 -0800

    Add asprintf() implementation for platforms without it

    Provides a portable implementation of this common allocating sprintf()
    API found in many, but not yet all, of the platforms we support.
    If the platform provides vasprintf() we simply wrap it, otherwise we
    implement it - either way callers can use it regardless of platform.

    Since not all platforms guarantee to NULL out the return pointer on
    failure, we don't either, and require callers to check the return
    value for -1.

    The old Xprintf() API is deprecated, but left for compatibility for now.

    The new API is added in a new header so that it can be used in parts of
    the server such as hw/xfree86/parser that don't include all the server
    headers.
Signed-off-by: Alan Coopersmith <alan.coopersmith@oracle.com>
Reviewed-by: Mikhail Gusarov <dottedmag@dottedmag.net>

Includes re-indentation changes from
9838b7032ea9792bec21af424c53c07078636d21.
Backported-to-NX-by: Mihai Moldovan <ionic@ionic.de>

Attributes GH PR #575: https://github.com/ArcticaProject/nx-libs/pull/575

Fixes: ArcticaProject/nx-libs#569
Fixes: ArcticaProject/nx-libs#573

Should be used instead of free() calls and will clear the pointer after
calling free(). This can prevent double-free or use-after-free errors.