tests/test-revert-unknown.out

Skip older monotone versions for tests.

test-convert-mtn is known to work with 0.37 and 0.38, but fails with
0.31 (Debian etch). hghave now skips all versions up to 0.31.

%% Should show unknown
? unknown
removing b
%% Should show unknown and b removed
R b
? unknown
%% Should show a and unknown
a
unknown