use pip requirements file directly as a pip argument
Merge branch 'pull_request.stanford_tokenizer' into pull_request.stanford_jenkins

Conflicts:
	nltk/parse/stanford.py
download nltk stanford dependencies
allow directory paths for environment variables in find_jar_iter()
move external dependencies to the 'third' directory
added environment variables to the stanford parser & tokenizers
added stanford environment variables to tox
added stanford parser doctests
Merge branch 'pull_request.stanford_jenkins' of https://github.com/jskda/nltk into develop