Implement EXTRA_maude_DEPENDENCIES for programs and libraries.

Implement EXTRA_maude_DEPENDENCIES for programs and libraries.

* 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.
Suggested by Eric Blake.

Signed-off-by: Ralf Wildenhues <Ralf.Wildenhues@gmx.de>