update: introduce a 'UpdateAbort' exception The 'postincoming' function used by 'hg pull --update' and 'hg unbundle' is catching 'Abort' exceptions to intercept failed update. This feel a bit too wide to me, so I'm introducing a more precise exception to specify update destination issues.

update: "deprecate" call to 'merge.update' without a destination Now that all internal callers pre-compute and set a destination at a higher level it feels like we can kill this API. This will allow us to simplify this function. However I feel like this is a bit too central and critical to break now. I'm adding a devel warning to let extension make catch this in the next cycle.

shelve: delete shelve statefile on any exception during abort When a user's repository is in an unfinished unshelve state and they choose to abort, at a minimum, the repo should be out of that state. We've found situations where the user could not leave the state unless manually deleting the state file. This fix ensures that no matter what exception may be raised during the abort, the shelved state file will be deleted, the user will be out of the unshelve state and they can get their repository into a workable condition.