Cmake test build (perl): Use File::Spec->rel2abs instead of abs_path()

Problem arises on fresh build, where the destination file is not yet defined.
In that case Cwd::abs_path() returns empty string, which fatal later on.
Set default to button which does _NOT_ discard data (part of #8787)
Merge branch 'master' of git.lyx.org:lyx
uk.po: update by Yuri
Merge branch 'master' of git.lyx.org:lyx
ar.po: update by Hatim Alahmadi
Merge branch 'master' of git.lyx.org:lyx
Beamer manual: add some notes on specific part behavior
Fix indentation for 'python -tt'
Implement file locking and apply to configure

Functions for file locking are added. They are used for ensuring that
for specified userdir only one LyX process runs configure.
ar.po: further updates
Do not attempt to set default master if we already have a parent
Update it.po
Prettify the tooltip for footnotes.
Also when not using tabs, do not open a file twice if already opened (part of #8787)
Properly name Cancel button (part of #8787)
Revert "Properly name Cancel button (part of #8787)"

This reverts commit aa5ef5bbbe0674e4e434882e5f2ffade9c68a7dc.
Fix CMake install of examples/thesis

I should have done this in f5cf21d7.
ctests: add dviluatex as a format that needs fonts

Documents in certain languages will only work with dviluatex
if fonts that support those languages are used.

This commit continues e690cfc4.
ctests: invert Hebrew LuaTeX tests