We no longer use custom Makefiles. This simplifies the setup, and fixes
some strange issues on my setup where I could run testgtk, but not test_rtrees
for instance.
N708-028
Remove all gtkextra-related files, since these are no longer supported in
gtk3.
N708-015
* src/Makefile.common.in, src/Makefile.in, src/tools/Makefile.in,
projects/Makefile, testgtk/Makefile.in, xml/Makefile,
docs/gtkada_ug/Makefile.in, docs/gtkada_rm/Makefile.in,
examples/Makefile (make install, DESTDIR): Allow installing into a staging
directory by assigning a path to the variable DESTDIR.