patch: pass in context objects into diffhunks() (API) It's a pretty low-level function and having the contexts in patch.diff() makes future patches easier. Differential Revision: https://phab.mercurial-scm.org/D5891

local test passed
addgroupcopy test passed
clone test passed
lowlevelcopy test passed
slicing test passed
issnapshot test passed
findsnapshot test passed