Attributes GH PR #767: https://github.com/ArcticaProject/nx-libs/pull/767

Agent PID 0 can be used for testing

By adding NX_CLIENT=<path to nxdialog> to the envrionment
certain actions in nx will open dialogs. If the options string contains
"menu=1" rootless windows will show a popup menu when the mouse hits
the center of the title bar offering session disconnect/terminatation.

Attributes GH PR #762: https://github.com/ArcticaProject/nx-libs/pull/762

Attributes GH PR #763: https://github.com/ArcticaProject/nx-libs/pull/763

Instead of using a pragma which will be valid for the whole file this
only affects the functions where it is actually required and supresses
"format string is not a string literal" warnings.

According to GCC documentation the second attribute parameter should
be 0:

"For functions where the arguments are not available to be checked
(such as vprintf), specify the third parameter as zero".

storage class specifier is deprecated and incompatible with C++17

Found via Travis CI

Attributes GH PR #788: https://github.com/ArcticaProject/nx-libs/pull/788

Attributes ArcticaProject/nx-libs#382

  commit cc5f09c86f7bea23b7546c3491b2c52ce8100a71
  Author: Alan Coopersmith <alan.coopersmith@oracle.com>
  Date:   Mon Jul 9 19:12:43 2012 -0700

    Use C99 designated initializers in various extension Replies
Signed-off-by: Alan Coopersmith <alan.coopersmith@oracle.com>
Reviewed-by: Keith Packard <keithp@keithp.com>
Tested-by: Daniel Stone <daniel@fooishbar.org>

Attributes ArcticaProject/nx-libs#382

  commit cdf5bcd420e5bcf4a4a24a275d3133a4e16ce41e
  Author: Alan Coopersmith <alan.coopersmith@oracle.com>
  Date:   Mon Jul 9 19:12:42 2012 -0700

    Use calloc to zero fill buffers being allocated for replies & events

    Ensures padding bytes are zero-filled
Signed-off-by: Alan Coopersmith <alan.coopersmith@oracle.com>
Reviewed-by: Keith Packard <keithp@keithp.com>
Tested-by: Daniel Stone <daniel@fooishbar.org>

Attributes ArcticaProject/nx-libs#382

Fixes ArcticaProject/nx-libs#399

reflect the version of libX11 we are basing on

Attributes GH PR 778: https://github.com/ArcticaProject/nx-libs/pull/778

 Fixes ArcticaProject/nx-libs#768.

 This reverts commit 889de46f.

 Fixes ArcticaProject/nx-libs#775.

 Fixes ArcticaProject/nx-libs#777.

Attributes GH PR #776: https://github.com/ArcticaProject/nx-libs/pull/776

The old unix-* session types are deprecated and will always
lead to a warning message "Unrecognized session type".

Internally there are only three session types: agent, proxy
and shadow, all the others are mapped to one of those three.

Attributes GH PR #774: https://github.com/ArcticaProject/nx-libs/pull/774

These keystrokes where the same as their viewport_scroll variants and made
the latter being disabled.

Fixes ArcticaProject/nx-libs#770