argp: merge changes from glibc Among other things, this should fix problems found by a Coverity scan and reported by Andrei Borzenkov: http://lists.gnu.org/archive/html/bug-gnulib/2016-01/msg00015.html http://lists.gnu.org/archive/html/bug-gnulib/2016-01/msg00016.html * lib/argp-ba.c, lib/argp-fmtstream.c, lib/argp-fmtstream.h: * lib/argp-fs-xinl.c, lib/argp-help.c, lib/argp-namefrob.h: * lib/argp-parse.c, lib/argp-pv.c, lib/argp-pvh.c, lib/argp-xinl.c: * lib/argp.h: Merge changes from glibc. * tests/test-argp-2.sh: Adjust to match new behavior.