unshelving into a tree with pending changes can make a mess; reverting makes it worse

[Jonathan Lange]

This is a big, ugly bug that should probably be split up. Here goes!

I just did this:
  * Make a bunch of tedious changes
  * Go away for a few days
  * Come back
  * Shelve changes
  * Merge in latest trunk
  * Forget to commit
  * Unshelve
  * Realize all the changes are mixed together
  * 'bzr revert' to undo the merge (lapse of reason)
  * Be very sad that my tedious changes are lost

Bazaar created some backup files (*~1~), but as best as I can tell, none of them have my changes.

[Martin Pool (mbp)]

sadness.

possible splits:

unshelve is like a merge so should follow similar rules to merge in discouraging you doing it if you have stuff already going on - except that it's probably more common to unshelve when you have a bit of pending work.

revert should be undoable.

all wt options should be optionally undoable.

backups should be dumped into say .bzr/trash rather than the wt, and done for all operations. (a kind of approximations to the preceding point.)

[Matthew Fuller (fullermd)]

> revert should be undoable.

I've thought a time or two that 'revert' should actually be
implemented as a special shelf. That's sorta what it does after all.