New APIs: set-program, get-program.

These set or get the program name in the handle.  Most programs
will never need to call this, since we set this, if possible,
using the glibc 'program_invocation_short_name(3)' feature.
Remove use of gnulib progname module.

It's simpler to use the glibc 'program_invocation_short_name(3)'
feature, and fall back to a generic solution.  Also remove risky
assignments to argv[0].
Update gnulib to latest.
Update translations from Transifex.