improvement; skip 'get_throttle' and 'put_throttle' in 'simulate=True' mode for speed-up

https://mediawiki.org/wiki/Special:Code/pywikipedia/11717
bug fix; enable import of 'Pillow' instead of 'PIL', see http://fedoraproject.org/wiki/Features/Pillow
improvement; enable usage of 'XMP' data from exiftool in order to get file history for categorization

https://mediawiki.org/wiki/Special:Code/pywikipedia/11718