D1133: test-clang-format: new test to verify that files stay clang-formatted

[durin42 (Augie Fackler)]

durin42 added inline comments.

INLINE COMMENTS

> ryanmce wrote in test-check-clang-format.t:1
> This test fails for me with errors about lz4revlog.
> 
> It feels like what we need here is a change similar to https://phab.mercurial-scm.org/rHG6c113a7dec52be38927b16962282ea660de0b03c, where we use the system hg to examine the local repository. Please reuse the `syshg` function here.

Derp, this is done.

REPOSITORY
  rHG Mercurial

REVISION DETAIL
  https://phab.mercurial-scm.org/D1133

To: durin42, #hg-reviewers, ryanmce
Cc: ryanmce, mercurial-devel