Fix (among other things) failure to boot when a CD is not inserted, caused by

Fix (among other things) failure to boot when a CD is not inserted, caused by
the new (correct) ASSERT in mutex acquisition in MmProbeAndLockPages, which
was erroneously being called from IoBuildAsynchronousFsdRequest at
DISPATCH_LEVEL.

The only correct course of action when calling IoBuildAsynchronousFsdRequest
at DISPATCH_LEVEL is to MmBuildMdlForNonPagedPool since the buffer must be
nonpaged (if the IRP completes synchronously, we'll still be at DISPATCH_LEVEL)
This is the case when direct io is done at DISPATCH_LEVEL using
IoBuildAsynchronousFsdRequest.

svn path=/trunk/; revision=34899