improve diagnostics for socket connections to fishd
configure/Makefile: respect $LIBS, remove some egregarious lies

 - expunge LIBS_COMMON, it doesn't get used anywhere
 - don't reset LIBS to empty
 - move the gettext test as every binary depends on it
 - only include one set of libraries
Prefer standard library lzma module if available

Prefer the standard library lzma module if available.  This change prevents
using the backports-lzma when it is installed for a version of Python that
already has the lzma module in its standard library.