Changed texclass to make attic/revtex.lyx compilable
Fix compilation on Solaris 11.1 (bug #8783)

Make sure that the configure script only checks features using the C++ compiler.

Also get rid of our last C files, since they are not compiled nor distributed anyway.
Do not keep the ancilliary *.pot files after they have been used
* INSTALL - Solaris build should work now.
Fix bug #8830: Compile error with disabled NLS

The Messages::gui_lang_ variable is instantiated in the '#ifdef ENABLE_NLS' block. To prevent compile problems, we should also instantiate it when NLS is disabled.
Remove layout and tex2lyx tests from make check

These tests need a built and configured LyX, so they do not work in the
distcheck target. They can now be called with make alltests.
Prevent build of <lang>.gmo in case of error.

Given erroneous <lang>.po file, this yields to error on first call
to make. Nonetheless a new <lang>.gmo file is created. The following
calls to make do not get an error.
This patch prevents the <lang>.gmo creation on error.

Problem spotted by Scott.