wv buildsys patch

Hi Dom,

this is a patch against wv that uses pkg-config's Requires: instead of
hardcoding the dependencies' Cflags and Libs in the .pc file. That way
the correct prefix is picked up automatically.
Another minor (related) cleanup is that i've consolidated things to
use DEPS_CFLAGS/LIBS (for pkg-config detected stuff) and
OPT_CFLAGS/LIBS for "manually" detected stuff. So it's no more needed
to put GSF_, LIBXML_, GLIB_, ZLIB_, ICONV_, WV_ and possibly other
CFLAGS and LIBS in each makefile template.

- Rob