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.

context: move _manifest from committablectx to workingctx committablectx had a _manifest implementation that was only used by the derived workingctx class. The other derived versions, like memctx and metadataonlyctx, define their own _manifest functions. Let's move the function down to workingctx, and let's break it into two parts, the _manifest part that reads from self._status, and the part that actually builds the new manifest. This separation will let us reuse the builder code in a future patch to answer _buildstatus with varying status inputs, since workingctx has special behavior for _buildstatus that the other ctx's don't have.

status: handle more node indicators in buildstatus There are several different node markers that indicate different working copy states. The context._buildstatus function was only handling one of them, and this patch makes it handle all of them (falling back to file content comparisons when in one of these states). This affects a future patch where we get rid of context._manifestmatches as part of getting rid of manifest.matches(). context._manifestmatches is currently hacky in that it uses the newnodeid for all added and modified files, which is why the current newnodeid check is sufficient. When we get rid of this function and use the normal manifest.diff function, we start to see the other indicators in the nodes, so they need to be handled or else the tests fail.

merge: remove uses of manifest.matches This gets rid of the manifest.matches calls in merge.py in favor of the new api. This is part of getting rid of manifest.matches since it is O(manifest).

copies: remove use of manifest.matches Convert the existing use of manifest.matches to use the new api. This is part of getting rid of manifest.matches, since it is O(manifest).