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
Is there an error message when trying to diff non-existing files?
+ hg diff not found
not: No such file or directory
found: No such file or directory
Is there an error message when trying to add non-existing files?
+ hg add not found
not: No such file or directory
found: No such file or directory