context: use wdirhex constant instead of calculating it Differential Revision: https://phab.mercurial-scm.org/D6143

split: use the new movedirstate() we now have in scmutil This avoids unnecessarily touching the working copy when splitting the parent of the working copy. That also makes the test-removeemptydirs.t case invalid, so we can just delete it. Differential Revision: https://phab.mercurial-scm.org/D6127

manifestcache: use `wcache` directory for manifest cache The manifest full text cache is tightly related to the working copy. We should use the `wcache` directory for it, instead of the `cache`. Otherwise, multiple shares would keep overwriting each other cache entry and we loose its benefit. This is also more consistent with the fact this cache file is protected by `wlock`.

manifestcache: protect write with `wlock` instead of `lock` The `wlock` is taken by both `update` and `commit` type operation. This would help persisting the cache more aggressively. An explicit test is introduced. However, we can already see the effect of this change on earlier test output.

manifestcache: clear the cache before testing the debug command Right now the cache is empty before this section of the test. However, we are about to improve the persistence of the cache (putting it under `wllock`, intead of `lock`). So we install the cleanup before.

manifestcache: abstract the filename in a class attribute This make the code clearer and simpler to update.

manifestcache: skip setup earlier if we don't have the lock There a no point preparing a closure if we are not going to use it.