[Gnash] --with-docdir

[strk]

I've fixed --with-docdir configure flag to reflect what's
specified in the help string. The macro in macro/docbook.m4
is always run, trying to detect locatoin of docbook.xsl
(I added /usr/share/sgml/docbook/stylesheet/xsl/nwalsh/ for
debian default path). --with-docdir=<PATH> overrides this.
--without-docdir (or --with-docdir=no) disables it.

Please try if everything works with your setup.
Note that I did not commit generated files, so you
need to invoke ./autogen.sh to get new things.

Thanks

--strk;