Merge branch 'po/rebase-preserve-merges'

Merge branch 'po/rebase-preserve-merges'

Various error messages that talk about the removal of
"--preserve-merges" in "rebase" have been strengthened, and "rebase
--abort" learned to get out of a state that was left by an earlier
use of the option.

* po/rebase-preserve-merges:
  rebase: translate a die(preserve-merges) message
  rebase: note `preserve` merges may be a pull config option
  rebase: help users when dying with `preserve-merges`
  rebase.c: state preserve-merges has been removed