Merge pull request #63 from OwenSmith/master

XenVif #44 and XenVbd #30
XenBus #47 and XenVbd #31

XenVbd #31 (Jun 12, 2014 12:36:26 PM)
	Prevent an assertion by triggering the DPC to poll frontend during pause.

XenBus #47 (Jun 12, 2014 11:36:56 AM)
    [CA-137823] Use interlocked calls when expanding grant tables

Signed-off-by: Owen Smith <owen.smith@citrix.com>