NFS server: Import various fixes from FreeBSD.

NFS server: Import various fixes from FreeBSD.

* Rev 228520: Honor NFSv3 commit call when count = 0. (delphij)

* Rev 228185: Enhance sequential access heuristic used for readahead
              and reuse it for writes as well.
        * Use a prime number for sequential detection table
        * Factor our sequential detection code
        * Ramp up sequential heurstic quickly based on IO size.

        This patch differs from the FreeBSD version in that we rapidly
        decay the sequential heuristic as in the original code and don't
        attempt to deal with reordered RPCs.

* Rev 159871: Size the NFS server dupreq cache on the basis of nmbclusters.
	This patch differs from the FreeBSD version in that we don't
	alter the desired cache size based on nmbcluster change events.

* Rev 116789: Bug in nfsrv_read() that caused the replies to certain NFSv3
short read operations at the end of a file to not have the "eof"
flag set. (iedowse)