pantsbuild/pants — pull request #575 by jsirois (2014-09-15 21:14:12+00:00)
Title: Make SourceRoot fundamentally understand a rel_path.

Add a factory for constructing a SourceRoot from a ParseContext
as a secondary means of creation and wire this up to core's
regiaster.py. Simplify a test as a result.

https://rbcommons.com/s/twitter/r/1036/