check-exec: write file in 'wcache' instead of 'cache' Some cache are relevant or affected by the working copy used. So the `.hg/cache` directory is not the best place for them because multiple shared repository can end up fighting over them. To address this issue, we introduce a new 'wcache' directory to host this kind of cache. The first user are the `checkisexec` type file. These files describe property of the working copy and fit the use-case well.

rebase: abort in-mem rebase if there's a dirty merge state In-memory merge uses the on-disk merge state, so we should not allow it run in-memory merge when the merge state is not clean. We should probably not use the on-disk merge state when running in-memory merge, but chaning that is not suitable for the stable branch. Differential Revision: https://phab.mercurial-scm.org/D5357