Branch b1_4

Branch b1_4
Multiple concurrent overlapping read+write on multiple SMP nodes
caused lock timeout during readahead (since 1.4.2).

Processes doing ll_page_matches() during readahead might match a lock
that hasn't been granted yet if there are overlapping and conflicting
lock requests pending.  The readahead process waits on ungranted lock
(original lock is CBPENDING), while OST waits for that process to cancel
CBPENDING read lock and eventually evicts client.

Caused by change to ll_page_matches() from bug 5654.
b=6469