Support Vala in non-recursive builds; more tests and fixes.

Support Vala in non-recursive builds; more tests and fixes.

* automake.in: Support Vala in non-recursive builds. Make sure
foo_VALAFLAGS really use used. Inject --library switch when building
Vala libraries.
* doc/automake.texi, NEWS: Document Vala support.
* m4/vala.m4: Rename AC_PROG_VALAC to AM_PROG_VALAC.
* tests/Makefile.am: Additional Vala tests.
* tests/vala.test: Also test VALAFLAGS support.
* tests/vala1.test: Test non-recursive Vala support.
* tests/vala2.test: Test _PKGNAME variables.
* tests/vala3.test: Test compiling of C code generated by Vala.

Signed-off-by: Mathias Hasselmann <mathias.hasselmann@gmx.de>
Signed-off-by: Ralf Wildenhues <Ralf.Wildenhues@gmx.de>