Fixup bootstrap script to point to https://pypi.python.org and fixup
plumbing to allow said-same for distribution resolution.

Also fixup an over-aggressive assert.  Some distributions, like
distribute 0.7.3, just serve as a dependency alias and export no top
level packages.
Merge pull request #156 from twitter/jsirois/pants/egg_woes

Fixup bootstrap script to point to https://pypi.python.org and fixup handling of meta-distributions
Report stats to server.

Specify stats_upload_url to pants.ini to receive a
POST form with 'cumulative_timings', 'self_timings',
'artifact_cache_timings', and 'run_info' params, each of
which have a JSON body.
Stats upload review fixes.
More review fixes.
Merge remote-tracking branch 'origin/master'