RFC: merge and revert - better diagnostic messages

[Jari Aalto]

the "bzr revert" page reads (0.11):

    To remove only some changes, without reverting to a prior version, use
    merge instead.  For example, "merge . --r-2..-3" will remove the changes
    introduced by -2, without affecting the changes introduced by -1.  Or
    to remove certain changes on a hunk-by-hunk basis, see the Shelf plugin.

Please also a case how to revert last changes:

    To remove only some changes, without reverting to a prior version, use
!   merge instead.  For example, "merge . -r-2..-3" will remove the changes
+    introduced by -2, without affecting the changes introduced by -1. If you
+   did a recent change, like merge, then you can revert the effect 
    by "-r<REV>..<REV - 1>". To remove certain changes on a hunk-by-hunk basis, 
    see the Shelf plugin.

- I believe the is type at "!", where "--r" should reads plain "-r".

Jari