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.