b=514: use IRQ-safe spin_lock calls for imp_lock, because it's handled from the

b=514: use IRQ-safe spin_lock calls for imp_lock, because it's handled from the
       interrupt context leading to __ptlrpc_free_req.

Use cmp instead of diff for quieter comparison of old and new build_version.

Replace non-portable spin_lock_irq with spin_lock_irqsave and co.  (C.f.
http://www.geocrawler.com/mail/thread.php3?subject=spin_lock_irq&list=9221 )