m4/nx-macros.m4: Add NX_STRICT_OPTION and NX_DEFAULT_OPTIONS macros (borrowed from X.org's xorg-macros.m4).

Attributes GH PR #501: https://github.com/ArcticaProject/nx-libs/pull/501

Fixes ArcticaProject/nx-libs#500

Attributes GH PR #499: https://github.com/ArcticaProject/nx-libs/pull/499

nxcomp/configure.ac: Don't rely on pkg-config alone when it comes to testing for presence of libjpeg shared lib and header files.

 Especially systems still using the IJG libjpeg implementation
 are likely to lack the libjpeg.pc file.
 .
 So this adds some alternative way of detecting if all libjpeg related
 build-dependencies are in place.

nxproxy/src/Makefile.am: Actually define nxproxy_CFLAGS, so the various compiler warning flags get enabled at build time of nxproxy.

Attributes GH PR #496: https://github.com/ArcticaProject/nx-libs/pull/496

 This change improves the situation in nxagent for the following
 issue:

 ```
 "XRenderCompositeTrapezoids builds RenderTrapezoids requests to composite the
 specified list of trapezoids to dst.  XRenderCompositeTrapezoids will split
 the list of trapezoids to build requests no larger than the maximum request
 size supported by the server.  This can create rendering artifacts as the
 precompositing done by RenderTrapezoids when a maskFormat is specified
 cannot span multiple requests."
 ```

 For more information see:
 https://lists.freedesktop.org/archives/xorg/2008-June/036124.html

 Fixes ArcticaProject/nx-libs#336.

Attributes GH PR #480: https://github.com/ArcticaProject/nx-libs/pull/480

nxcomp/src/Loop.cpp: Don't mix using global proxyFD and a local p(roxy)FD variable (in WaitForRemote() and ConnectToRemote()). Rename local variable name.

nxcomp/src/Loop.cpp: Don't reuse global variable names as function parameters in SetupDisplaySocket().

nxcomp/src/Loop.cpp: Avoid duplicate usage of proxyFD (global variable) and *proxyFD (function parameter).

debian/rules: Drop override_dh_clean target. Not required anymore, as configure files get removed correctly now.

nxcomp/configure.ac,m4/nx-macros.m4,nxcomp/src/Socket.h: Use AC_CHECK_TYPES to detect if type 'in_addr_t' is available.

nxcomp/configure.ac: Re-add previously available configure options --with-valgrind and --with-info as renamed options --enable-valgrind and --enable-debug.

Attributes GH PR #484: https://github.com/ArcticaProject/nx-libs/pull/484

This way one can easily pass options to nxagent run as Xnest
replacement without having to create a temporary options file. Please
note that it is not of much use for normal sessions. Options passed
like this cannot be changed after startup so a reconnect may not work
as expected.

Fixes ArcticaProject/nx-libs#476

Do not use global variables where it is not necessary.

Attributes GH PR #487: https://github.com/ArcticaProject/nx-libs/pull/487

Fixes ArcticaProject/nx-libs#486

Attributes GH PR #474: https://github.com/ArcticaProject/nx-libs/pull/474

nxcompshad: Rewrite Logger class methods to properly take advantage of the 'gnu_printf' format attribute.