Documentation/Makefile: add missing xsl dependencies for manpages

Documentation/Makefile: add missing xsl dependencies for manpages

These stylesheets very rarely change, but when they do, it really helps
if the manpages depend on them. We're casting the net a bit too wide
here, since we'll only ever use a subset of the stylesheets, but since
these files change so rarely, that should be ok. It's better than
missing a dependency.

Observe that manpage-base-url.xsl is a generated file, so we need to
list it explicitly, besides the `wildcard` expression we're adding here.

Signed-off-by: Martin Ågren <martin.agren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>