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.
adding aupdating working directory1 files updated, 0 files merged, 0 files removed, 0 files unresolvedadding bpushing to ../aabort: could not lock repository ../a: Permission denied