Summary:
Catnotate is a version of hg cat with output annotated with file name and line
number. Such output is very useful when running hg cat on multiple files
(for example in commit hooks).
Test Plan: unit tests
Reviewers: #sourcecontrol, pyd, mpm, durham, rmcelroy
Reviewed By: rmcelroy
Differential Revision: https://phabricator.fb.com/D2497470
Signature: t1:2497470:1444842798:9192ef3ef1603d068e7f38777def81a43bed0414
