Fix hg clone race with writer
Most read operations in hg don't need locks because we order reads and
writes for consistency. Clone is an exception to this as we're copying
entire file histories and could end up with more file history copied
than we have commits.
For now, make clone take a lock on the source repo. Non-hardlinked
clone should eventually be changed to use lockless pull.
+ hg init
+ hg addremove
adding foo
+ hg commit -m 1
+ hg verify
checking changesets
checking manifests
crosschecking files in changesets and manifests
checking files
1 files, 1 changesets, 1 total revisions
+ hg clone . ../branch
+ hg co
+ hg commit -m 2
+ hg pull ../branch
pulling from ../branch
searching for changes
adding changesets
adding manifests
adding file changes
added 1 changesets with 1 changes to 1 files
(run 'hg update' to get a working copy)
+ hg verify
checking changesets
checking manifests
crosschecking files in changesets and manifests
checking files
1 files, 2 changesets, 2 total revisions
+ hg co
foo
bar
+ hg manifest
6f4310b00b9a147241b071a60c28a650827fb03d 644 foo