Use unsigned version format.
This way can use one additional bit, and when encountering invalid revlogs
with the first bit set don't produce python warnings or strange error messages.
0 files updated, 0 files merged, 0 files removed, 0 files unresolved
0 files updated, 0 files merged, 0 files removed, 0 files unresolved
adding b
0 files updated, 0 files merged, 0 files removed, 0 files unresolved
adding b