index: don't include nullid in the internal "length" field
This is a follow-up to
781b2720d2ac (index: don't include nullid in
len(), 2018-07-20). I intentionally didn't update the "index stats",
so it will also not include the space for nullid after this patch.
Differential Revision: https://phab.mercurial-scm.org/D4162
tests: add test coverage for revlogindex[-1] which was previously missing
Differential Revision: https://phab.mercurial-scm.org/D4184
context: safegaurd from 'lx' being passed as file flag in manifest
Follows up for
d558e53cd6b619d5f671a7580513bfc66a398eac.
Differential Revision: https://phab.mercurial-scm.org/D4259
debugcommands: urlerror only has a read() method in Python 2
Differential Revision: https://phab.mercurial-scm.org/D4258