hook: protect commit hooks against stripping of temporary commit (issue4422)

History rewriting commands like histedit tend to use temporary
commits. They may schedule hook execution on these temporary commits
for after the lock has been released. But temporary commits are likely
to have been stripped before the lock is released (and the hook run).
Hook executed for missing revisions leads to various crashes.

We disable hooks execution for revision missing in the repo. This
provides a dirty but simple fix to user issues.

--HG--
branch : stable