server: ensure the incoming request falls under the prefix value
Prior to this, the first test asserted in wsgiref.validate.check_environ()
saying PATH didn't start with '/', but the second test served up the repo. The
assertion was just added in this cycle (though the value of PATH is still wrong
without the assertion). Allowing access to the repo at any URL outside of the
prefix is a long standing bug. This also affected hgwebdir, at least when used
via --subrepo.
Paths are not being canonicalized, so accesses to things like 'foo/../bar' will
get tossed out here, unless the prefix also matches.
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).