Speed improvement on GAAClusterer

New improved vectorized version of GAAClusterer that is orders of magnitude
faster than the previous one.
Updates to GAAClusterer so that the new cluster_vectorspace function
conforms to PEP 8.
Readability changes and comment additions to GAAClusterer

- Removed _average_similarity and imported cosine_distance
- Added _average_link to be clear about how the distance
  matrix is updated after merge
- Changed sim to dist since we are using distances instead
  of similarities now
Renaming _average_link to _merge_similarities
updated doctest (new order of items)
Merge pull request #418 from angeloskath/master

Speed Improvements in GAAClusterer
Explicitly mention setuptools 0.6 in install.rst

Setuptools merged with Distribute in 0.7. I think setup.py needs to be migrated to 0.7?
updates for new release 3.0a2
fixed spurious errors in semantics.doctest and drt.doctest
fixed spurious errors in logic.doctest and drt.doctest
fixed chunk/regexp.py chunk parser usage examples
Merge pull request #1 from nltk/master

Updating
use _im_class instead of im_class to avoid conflict with nose.suite.ContextSuiteFactory.ancestory seeing the compat module as a class
Merge pull request #429 from jskda/master

nltk fixes
fixed xml encoding detection bug, can be reproduced by the following code: "from nltk import book"
Merge pull request #430 from jskda/master

PY3 fixed xml decoding detection bug
PY3: fix nltk.classify.tadm
rename compat._im_class to compat.get_im_class because it is not private
Lowest Common Hypernyms Change & Tests

- Set lowest_common_hypernyms to use max_depth by default
- Updated wup_similarity() to use min_depth with LCH
- Added a tests file for wordnet (only tests lowest_common_hypernyms()
at the moment)
- Added an additional LCH example to demo() which illustrates a case
where a target synset is also the LCH for itself and another synset
doctest and docstring updates