All objects defining $(OBJS) will get them and *.a deleted during
make clean.
The all, clean and install rules now implicitly imply their -recursive
counterparts - those will just do nothing in case of $(SUBDIRS) not
defined, so that's ok.
The root makefile is converted as well as some leaf Makefiles. This
also brings in the required infrastructure and adjusts configure.in
appropriately.
I converted only makefiles containing no configurable stuff, since
that'll require more consideration yet.
