Treat v:shell_error >= 2 as "not version controlled" for AccuRev
Treat v:shell_error >= 2 as "not version controlled" for AccuRev

When a user isn't logged in, "accurev diff" will return an exit code of
52.  Since the only well defined values are 0 or 1, treat anything else
as unversioned.

mhinz/vim-signify