tests: Enable rhg fallback to Python by default in tests...
tests: Enable rhg fallback to Python by default in tests
This premise of `run-tests.py --rhg`: fallback should make
`rhg` behave the same as `hg`, except faster in some cases.
To test run the whole test suite with installed `rhg` as `hg`
and with fallback enabled.
Differential Revision:
https://phab.mercurial-scm.org/D10187
