Load libNX_X11 / faked libX11 via RPATH setting rather than fidgeting with LD_LIBRARY_PATH in the nxagent wrapper script.

 Fixes ArcticaProject/nx-libs#225.

  SHLIBDIR -> Points to the system's official library folder.
  USRLIBDIR -> In NX, this variable (amongst others) is used to set
               the executables RPATH (if enabled), so pointing this
               to SHLIBDIR/nx-X11.

debian/rules: Don't manually override SHLIBDIR via the dh_auto_build call. The default in the main Makefile should work fine.

nx-libs.spec: Don't manually override SHLIBDIR via the .spec file. The default in the main Makefile should work fine.

Makefile: Align variable names USRLIBDIR, SHLIBDIR (and NX_DIR) with nx-X11 internal naming schemes (and use /usr/<lib>/nx/X11 rather than /usr/<lib>/nx-X11).

Attributes GH PR #289: https://github.com/ArcticaProject/nx-libs/pull/289

nx-X11/include/Xos_r.h: Drop one _POSIX_REENTRANT_FUNCTIONS macro block, where offenders AIXV3, AIXV4 and __osf__ are gone now.

 Backported from X.org:

 From f93d10ce9bb4a6de83b561f44fb7b046def16234 Mon Sep 17 00:00:00 2001
 From: Daniel Stone <daniel@fooishbar.org>
 Date: Mon, 6 Nov 2006 18:33:45 +0200
 Subject: dix: remove staggeringly broken vendor workarounds
Backported-to-NX-by: Mike Gabriel <mike.gabriel@das-netzwerkteam.de>

 Relates to ArcticaProject/nx-libs#275.

 Relates to ArcticaProject/nx-libs#275.

 Relates to ArcticaProject/nx-libs#275.

 Fixes ArcticaProject/nx-libs#288.

 Fixes ArcticaProject/nx-libs#274.

 Fixes ArcticaProject/nx-libs#273.

 Fixes ArcticaProject/nx-libs#272.

 Fixes ArcticaProject/nx-libs#271.

Attributes GH PR #323: https://github.com/ArcticaProject/nx-libs/pull/323

Fixes ArcticaProject/nx-libs#293

Attributes GH PR #315: https://github.com/ArcticaProject/nx-libs/pull/315

debian/copyright{,.in}: Adopt from Debian's upload candidate, being DEP-5 compliant and up-to-date for 3.5.99.3.

 Fixes ArcticaProject/nx-libs#2.

Makefile: Don't create superfluous symlink for libX11.so -> ../libNX_X11.so. The libNX_X11.so is only required at build time, so need to use it for faking libX11.so in nxagent.

 Fixes ArcticaProject/nx-libs#286.

 Fixes ArcticaProject/nx-libs#303.

Attributes GH PR #307: https://github.com/ArcticaProject/nx-libs/pull/307

Attributes GH PR #304: https://github.com/ArcticaProject/nx-libs/pull/304

roll-tarballs.sh: Adapt to recent changes in nx-libs, keep legacy support for older 3.6.x and 3.5.x releases.

Attributes GH PR #299: https://github.com/ArcticaProject/nx-libs/pull/299