This patch changes the last user of recursive locking so that
it no longer needs this feature and removes it from the glock
layer. This makes the glock code a lot simpler and easier to
understand. Its also a prerequsite to adding support for the
AOP_TRUNCATED_PAGE return code (or at least it is if you don't
want your brain to melt in the process)

I've left in a couple of checks just in case there is some place
else in the code which is still using this feature that I didn't
spot yet, but they can probably be removed long term.
Signed-off-by: NSteven Whitehouse <swhiteho@redhat.com>