Make nxproxy and nxagent print an arbitrary version number by running
make NX_VERSION_CUSTOM="myvers". nxagent and nxproxy will then show
this in addition to the original version number:

NXPROXY - Version myvers (3.5.99.22)
NXAGENT - Version myvers (3.5.99.22)

Fixes ArcticaProject/nx-libs#606

One cannot simply pass down a va_list to another function that expects
variable arguments ("..."). The prototype of the called functions must
expect a va_list argument instead.

This fixes segfaults that happen e.g. after compiling X11.cpp with
TEST and effectively reverts 59e829f3.

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".

Found via Travis CI

nxcomp{,shad}/configure.ac: replace versionating non-portable sed construct with hopefully more portable awk construct.

nxcompshad/{configure.ac,src/Makefile.am}: only enable new ELF dtags if target system actually is ELF-based.

Same method as used in the previous commit, but easier done thanks to
autotools and libtool.

Fixes: ArcticaProject/nx-libs#610

Fixes ArcticaProject/nx-libs#572

Automake older than version 1.11 does not support dist-xz. No workaround
possible via a feature check, as far as I can tell.

Fixes ArcticaProject/nx-libs#530

nx{comp{,shad},proxy}: add configure flag --enable-cxx11 to enable and setup optional C++11 support.

Use AX_CXX_COMPILE_STDCXX(_11) from autotools archive.

Note: should only be used in tandem. Make sure that each component
either uses the C++11 ABI or none uses it. Mixing and matching libraries
and binaries with different C++ ABIs might lead to weird errors.

 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.

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

nxcompshad/src/Shadow.cpp: Drop duplicate prototype for NXShadowRemoveAllUpdaters(). Already in Shadow.h.

nxcompshad/src/Regions.h: Avoid warning: ‘typedef’ was ignored in this declaration. Drop typedef declaration from _XRegion struct.

When installing nxcompshad, directory user and group ownership were
forced to be root. That precluded installations by non-root users.

Now, they are not forced.

nxcompshad/Shadow.cpp: Use EBADF instead of EBADFD (which is not portable to GNU/Hurd and GNU/kFreeBSD).

 We use the error code (and its underlying message for
 generating log errors and their textual messages. So,
 in theory, we could use any error code here. Thus,
 choosing the once closest to EBADFD while being
 portable to non-Linux systems.

Per-file copyright notices: Update copyright information in file headers that NoMachine placed there own copyright statement in.

 Drop other LICENSE files added by NoMachine scattered all over the code tree.

 One COPYING file in the project's base folder is sufficient.