[Xapian-devel] Tinderbox tweaks

[Olly Betts]

I've tweaked the tinderbox build scripts so that they'll automatically
try to build and use a private copy of zlib if it doesn't seem to be
installed and to build and test the Search::Xapian perl bindings:

http://www.oligarchy.co.uk/tinderbox/xapian/status.html

There are still a few kinks to sort out, but hopefully this can help us
catch any portability issues before the release.

Cheers,
    Olly