localrepo: add optional validation (defaults to off) for incoming changes
This verifies that all manifests are present for incoming changes,
and all files for those manifests are also present. This is a simple
first-pass, and could be better, but seems like a valuable thing to
have, as I've seen pushes in the past that propagated revlog corruption.
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
removing b
created new head
% should abort
abort: crosses branches (use 'hg merge' to merge or use 'hg update -C' to discard changes)
% should succeed
1 files updated, 0 files merged, 0 files removed, 0 files unresolved