This subcommand is disabled by default because of bugs that make some test fail.
Enable it in the rest of the tests in order to avoid regressing them.
As with RHG_ON_UNSUPPORTED, an environment variable is used instead of
a configuration file and HGRCPATH because some tests override HGRCPATH.
Running unset RHG_STATUS at the start of a test restores the default of
rhg status being disabled. Hopefully it can be increasingly removed
from test files as bugs are fixed.