Make CoqIDE compile with windows (Closes: 3573)

CoqIDE seems to work, but for random pauses that make you think
of a thread deadlock, but then, after a few seconds, things make
progress again.  This happens only seldom on my virtual machine.
Reimplementing the clearbody tactic.
Removing the old implementation of clear_body.
Revert the two previous commits. I was testing in the wrong branch.