Attributes GH PR #489: https://github.com/ArcticaProject/nx-libs/pull/489

 This code can be reactivated any time in the future once
 some potential maintainer turns up and makes this work
 on the MS Windows / Cygwin platform.

Attributes GH PR #488: https://github.com/ArcticaProject/nx-libs/pull/488

nx-X11/programs/Xserver/Render.c: Re-introduce nxagentGlyphsCleanup() from libNX_Xrender's formerly removed XRenderGlyphsCleanup().

Attributes GH PR #498: https://github.com/ArcticaProject/nx-libs/pull/498

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).