rebase: add short -k option for --keep

histedit and strip already have a short option for keep, so this makes the
interface more consistent

hgext/rebase.py

@@ -67,7 +67,7 b' def _makeextrafn(copiers):'
     ('e', 'edit', False, _('invoke editor on commit messages')),
     ('l', 'logfile', '',
      _('read collapse commit message from file'), _('FILE')),
-    ('', 'keep', False, _('keep original changesets')),
+    ('k', 'keep', False, _('keep original changesets')),
     ('', 'keepbranches', False, _('keep original branch names')),
     ('D', 'detach', False, _('(DEPRECATED)')),
     ('i', 'interactive', False, _('(DEPRECATED)')),

tests/test-rebase-scenario-global.t

@@ -397,7 +397,7 b' Source on have two descendant heads but '
   abort: can't remove original changesets with unrebased descendants
   (use --keep to keep original changesets)
   [255]
-  $ hg rebase -r '2::8' -d 1 --keep
+  $ hg rebase -r '2::8' -d 1 -k
   rebasing 2:c9e50f6cdc55 "C"
   rebasing 3:ffd453c31098 "D"
   rebasing 6:3d8a618087a7 "G"