fumount: Fix BUG_ON in __fput_sync

__fput_sync would do a BUG if the file was still associated with
a thread, but that's still the case in a fumount.  So don't do
that bug if the file is in a fumount.

Signed-off-by: Corey Minyard <cminyard@mvista.com>
fumount: Remove the exec file

If a fumounted file is the exe file for an mm, remove it.

Signed-off-by: Corey Minyard <cminyard@mvista.com>