expression simplification in nltk.sem.logic
server url option in downloader's command line arguments
fixed problem in downloader where some zips might not have all directories in the zip info list, hence not returned by namelist()
Revert "python 2.7 pickle compatibility", since this is a pickle.dump bug, not a pickle.load bug, thanks to kmike for pointing this out

This reverts commit d8d7ea1fa142f6be1a9634968023509bff7b42c8.
fixed bugs in resource url normalization & added doctests
fixed invalid relative file URI usage in doc tests: the file protocol does not allow relative paths
fixed python 3 encoding bugs in corpus.doctest and allow it to succeed on windows
python 2.6 windows doesn't always print xml elements starting with '0x'