XFS updates for 3.0-stable

[Christoph Hellwig]

Two more updates for 3.0-stable.  The first one is a simple fix that
just went to mainline and is a real no brainer.  The second once is
more borderline vs the stable criteria - it's very small but not a bug
fix in the traditional sense but rather fixing an absymal low
performance due to an errornous synchronous transaction.  This really
shows up badly in various cloud and cluster storage scenarious, and has
already been backported to at least on of the enterprise distribution
kernels.