Change Parso to use cPickle instead of pickle when reading/writing the
cache, which speeds up the cache significantly.
In Python 2, cPickle is up to 1000 times faster than pickle. (In Python
3, if you "import pickle", you are actually getting cPickle.)
As is the convention, the code tries to import cPickle, and if that
fails, it falls back to pickle.
This has a big impact for users of jedi-vim, since in many cases Vim
uses Python 2.
Any caller of Parso can specify a cache path, and if none is specified,
parso will fall back to a default.
Parso's code to read a file from the cache handled this correctly; but
its code to write a file to the cache had a bug -- any override of the
default was ignored.
In the case of Jedi, this is a significant problem, since Jedi overrides
the default. The result is that files will be written to the cache, but
will then never be found when reading from the cache.
Mike Morearty