subrepo: add tests for git rogue ssh urls (SEC)
'ssh://' has an exploit that will pass the url blindly to the ssh
command, allowing a malicious person to have a subrepo with
'-oProxyCommand' which could run arbitrary code on a user's machine. In
addition, at least on Windows, a pipe '|' is able to execute arbitrary
commands.
When this happens, let's throw a big abort into the user's face so that
they can inspect what's going on.
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).