Our syntax checker missed all-lower-case variables (this will
be fixed by the next .gnulib update).  Additionally, anywhere
that we mix in-tree files with generated files, automake recommends
listing builddir prior to srcdir for VPATH builds.

* src/Makefile.am (*_la_CFLAGS): Favor $(top_srcdir).
(INCLUDES): Likewise, and follow automake recommendations on
builddir before srcdir.
* python/Makefile.am (INCLUDES): Swap directory order.
* tests/Makefile.am (INCLUDES): Likewise.
* tools/Makefile.am (INCLUDES): Likewise.
* daemon/Makefile.am (INCLUDES): Likewise.
(libvirtd.init, libvirtd.service): Favor $().
* examples/hellolibvirt/Makefile.am (hellolibvirt_LDADD):
Likewise.
* examples/openauth/Makefile.am (openauth_LDADD): Likewise.
* examples/dominfo/Makefile.am (INCLUDES): Drop dead include.
* examples/domsuspend/Makefile.am (INCLUDES): Likewise.