uncommit: add a new flag `--revert` to discard wdir changes after uncommit This patch adds a new flag to `hg uncommit` using which one can discard the wdir changes which are left after the operation. Both the changes, the ones which were before the uncommit and the ones which were added to wdir as a result of uncommit as cleared out.

#require test-repo pyflakes

Copied from Mercurial core (60ee2593a270)

  $ cd "`dirname "$TESTDIR"`"

run pyflakes on all tracked files ending in .py or without a file ending
(skipping binary file random-seed)

  $ hg locate 'set:(**.py or grep("^#!.*python")) - removed()' 2>/dev/null \
  > | xargs pyflakes 2>/dev/null