[IBAL] This patch fixes IBAL object destruction. It does the following:

[IBAL] This patch fixes IBAL object destruction.  It does the following:

1. Removes forcing synchronous destruction for user-mode exported objects.  This isn't needed, and slows down cleanup of the object hierarchy.

2. Clears the user-mode exported handle from the handle table before invoking the 'destroying' callback of an object, so that all further reference on the object will fail.  Currently, an IOCTL could take a reference on an object after the 'destroying' callback has returned.

Signed-off-by: Fab Tillier <ftillier@microsoft.com>
git-svn-id: svn://openib.tc.cornell.edu/gen1/trunk@1329 ad392aa1-c5ef-ae45-8dd8-e69d62a5ef86