Summary:
Be a better citizen under system python path.
Fix all tests issues and change setup.py to use glob pattern to include
all extensions.
Test Plan:
Run tests and `make local`.
Also build and install the package and run `hg sl` in major repos.
Reviewers: #mercurial, ttung, rmcelroy
Reviewed By: rmcelroy
Subscribers: rmcelroy, durham, mjpieters
Differential Revision: https://phabricator.intern.facebook.com/D3534311
Signature: t1:3534311:1468275426:fe122646c8bd6c541e1889e73e9df28f86747ff2
