Updated INSTALL doc to include Python Imaging Library requirement

Ignore-this: 908fb6afa08a561dfc510a10fc65da81

darcs-hash:20091130100425-56b4d-510141150aba2553c7d761b874e9c5d3884277c2
Fix xcap_icon to download icons with original filename

Ignore-this: af8e396219f892a3fd0da75b79c502e6

darcs-hash:20091130111646-56b4d-b56e5f48ece96ccacee24968d84c536910adc86f