progs, libs: implement EXTRA_foo_DEPENDENCIES

progs, libs: implement EXTRA_foo_DEPENDENCIES

Backported from commit `v1.11-377-g6edafbb'.

The feature implemented by that change is quite unobtrusive, so
adding it to a maintenance release is acceptable.  Also, there
have been requests from real-world users for this feature since
it has been implemented in master; see automake bug#9320:
 <http://debbugs.gnu.org/cgi/bugreport.cgi?bug=9320>
and this short discussion on the automake list:
 <http://lists.gnu.org/archive/html/automake/2010-11/msg00099.html>
It would be a pity to make such users wait even more (until
Automake 1.12 is out) before they could start using this feature.
Thus we backport it, so that it will appear in the next maintenance
version of automake (1.11.3).

* automake.in (handle_programs, handle_libraries)
(handle_ltlibraries): Mark EXTRA_*_DEPENDENCIES as recognized.
* doc/automake.texi (Linking, Program and Library Variables)
(LIBOBJS): Document EXTRA_*_DEPENDENCIES.
* lib/am/library.am (%LIBRARY%): Also depend on
$(EXTRA_%XLIBRARY%_DEPENDENCIES).
* lib/am/ltlibrary.am (%LTLIBRARY%): Also depend on
(%XLTLIBRARY%_DEPENDENCIES).
* lib/am/program.am (%PROGRAM%%EXEEXT%): Also depend on
$(EXTRA_%XPROGRAM%_DEPENDENCIES).
* tests/extradep.test, tests/extradep2.test: New tests.
* tests/Makefile.am (TESTS): Update.
* NEWS: Update.