install-reloc: Support multi-binary installation.

* build-aux/install-reloc: Support installing multiple programs in
one invocation, as done by Automake starting with commit
4295fe33eb23f (Multi-file install for PROGRAMS.).  From Bruno
Haible <bruno@clisp.org>, archived at
http://lists.debian.org/debian-bsd/2012/05/msg00032.html.
Reported by Sylvain <beuc@gnu.org>.
maint.mk: get current gnulib revision correctly.

* top/maint.mk (gnulib-version): Use git rev-parse to get the
current HEAD revision.

Signed-off-by: Gary V. Vaughan <gary@gnu.org>
maint.mk: fix "release" target to build _version

This fixes a bug in README-release whereby following the outlined
steps, one would publish a tarball whose programs would report
--version output not consistent with the package version number.
This bug caused grep-2.15 to produce a grep program whose
--version option made it print 2.14.56-1e3d rather than 2.15.
* top/maint.mk (release): Making this target build "_version"
ensures that the new version number is reflected in configure.
Revert "error: make the module depend on vfprintf-posix"

This reverts commit 88e5b4d4641f294d8f824d770c9c55a1abe49768.

The GPL 'error' module is used by some of the gnulib testsuites;
and for some projects that use LGPL 'vasnprintf' in their lib/
directory, having 'error' depend on GPL 'vfprintf-posix' meant
that compilation breaks for those projects:

autoreconf: running: aclocal -I m4 --force -I m4
missing file gnulib/tests/vasnprintf.c
configure.ac:135: error: expected source file, required through
AC_LIBSOURCES, not found
m4/gnulib-comp.m4:518: gl_INIT is expanded from...
configure.ac:135: the top level
autom4te: /usr/bin/m4 failed with exit status: 1

I suspect that the problem encountered on OS/x was a warning from
gcc complaining about inconsistent use of __attribute__((__format__
__printf__)) vs. ((__format__ __gnu_printf__)); so perhaps the
real fix is to teach error.h to copy the extra care taken by
stdio.h with regards to whether merely system or full GNU printf
specifiers are being handled.  But without actually reproducing
that situation myself, the easiest action for now is to just revert
the dependency that violates the 'Comment' section of vfprintf-posix.
maint.mk: restore functionality removed by recent change

Sunday's change, v0.0-8062-g6b24f60, may have appeared correct from
the context of a shallow-cloned gnulib repository: "git describe"
would fail in such a directory.  However, that change made it so
the reported gnulib revision no longer includes the version number
or a commit count, even when run from a full clone.
* top/maint.mk (gnulib-version): Use the full "git describe"
output when possible, e.g., the form above, rather than the
abbreviated, no-tag, no-commit-count string, and fall back to
using a 10-byte hash, rather than the default minimal-length
hash prefix, since while the minimal-length one may be fine today,
it is likely not to be unique for very long.
gnulib-tool: protect against CDPATH

* gnulib-tool: Many "cd" built-in functions print a directory name
to stdout when CDPATH is set, e.g.,
  $ bash -c 'CDPATH=/; cd tmp'
  /tmp
Unset it, when possible.  Prompted by a comment from Bruce Korb.