CONTRIBUTING

checkexec: create destination directory if necessary

Since 460733327640, a "share" use the cache of the source repository. A side
effect is that no `.hg/cache` directory exists in the "share" anymore. As a
result, the checkexec logic can't use it to create its temporary file and have
to use the working copy for that.

This is suboptimal, it pollutes the working copy and prevents them to keep the
file around in cache. We do not want to use the cache directory for the share
target, it might be on a different file system.

So instead, we (try to) create the directory if it is missing. This is a
simple change that fixes the current behavior regression on stable.

On default, we should probably ensure the proper directories are created when
initializing the repository. We should also introduce a 'wcache' directory to
hold cache file related to the working copy. This would clarify the cache
situation regarding shares.

The tests catch a couple of other affected cases.

Our full contribution guidelines are in our wiki, please see:

https://www.mercurial-scm.org/wiki/ContributingChanges

If you just want a checklist to follow, you can go straight to

https://www.mercurial-scm.org/wiki/ContributingChanges#Submission_checklist

If you can't run the entire testsuite for some reason (it can be
difficult on Windows), please at least run `contrib/check-code.py` on
any files you've modified and run `python contrib/check-commit` on any
commits you've made (for example, `python contrib/check-commit
273ce12ad8f1` will report some style violations on a very old commit).