Fix license string according to http://spdx.org/licenses/.

https://www.mail-archive.com/lyx-devel@lists.lyx.org/msg184749.html
* sk.po: spellcheck changes
Give more tips in beamer-article.lyx
Fix a comment
Update ctests to reflect inputenc changes

There were changes to inputenc and luainputenc that are now
released in Tex Live 2014 that affect several exports. Some
exports that produced good PDFs now fail. Others that produced
incorrect PDFs (with gibberish) now correctly fail. Several
IEEEtran-* exports failed before and now export correct PDFs.

For more information, see

  http://tug.org/pipermail/tex-live/2014-May/035338.html
  https://www.mail-archive.com/lyx-devel@lists.lyx.org/msg184435.html
ctests: Use regular expressions
Cmake tests: Optimizing the cmake configuration time

The configuration time suffers mostly on checking, which of the export tests
is to be reverted.
1.) There is a new configuration flag now, "LYX_ENABLE_EXOPRT_TESTS.
   If not set (default) no export tests are created.
2.) If set, then the optimization halves the time needed for creation of tests.

The effect on my side:
        a.) Until now the time was:        ~ 26 seconds
        b.) The optimized time is now:     ~ 16 seconds
        c.) With not enabled export tests: ~  5 seconds
CMake: full path of an include needed for ver <3.0
Remove an incorrect/expired FIXME

Both Richard and JMarc think it is incorrect. See
  https://www.mail-archive.com/lyx-devel@lists.lyx.org/msg184758.html