mdiff: compute newlines-splitted texts within _unidiff There is no reason to compute splitted texts l1, l2 in unidiff() before calling _unidiff as they are only used with the latter function.

dispatch: add pagination of two more help cases I missed these in the last round anf Yuya spotted them in review. Thanks!

help: avoid mutating passed-in `keep` list in `formattedhelp`

extensions: use [0:1] slice on config path instead of [0] This behaves the same in Python 2 and Python 3, even though the path is a bytes.

extensions: use inspect module instead of func_code.co_argcount Fixes the extsetup argspec check on Python 3.

treemanifest: add tests covering hg diff of partial trees Previously the hg files tests also covered the logic (i.e. treemanifest.matches) that governed how hg diff limited its diff. In a future patch we will be switching treemanifest.diff() to have a custom implementation, so let's go ahead and add equivalent test coverage for hg diff.

context: remove uses of manifest.matches This removes the uses of manifest.matches in context.py in favor of the new manifest.diff(match) api. This is part of removing manifest.matches since it is O(manifest). To drop the dependency on ctx._manifestmatches(s) we transfer responsibilty for creating status oriented manifests over to ctx._buildstatusmanifest(s). This already existed for workingctx, we just need to implement a simple version for basectx. The old _manifestmatches functionality is basically identical to the _buildstatusmanifest functionality (minus the matching part), so no behavior should be lost.

context: remove assumptions about manifest creation during _buildstatus Previously we called self.manifest() in some cases to preload the first manifest. This relied on the assumption that the later _manifestmatches() call did not duplicate any work the original self.manifest() call did. Let's remove that assumption, since it bit me during my refactors of this area and is easy to remove.