FreeBSD 9.1: Warning fixes

Fix warnings caused by some changes in FreeBSD 9.1:

 - afs_cmount takes a uint64_t for flags instead of an int
 - vn_rdwr takes a ssize_t* for resid instead of an int*

[kaduk@mit.edu: rebase onto master and use fine-grained version checks]

Change-Id: I03ab805a625790004a910df96b96aeda1121e2a7
Reviewed-on: http://gerrit.openafs.org/8922
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Garrett Wollman <wollman@csail.mit.edu>
Reviewed-by: Chas Williams - CONTRACTOR <chas@cmf.nrl.navy.mil>
Reviewed-by: Derrick Brashear <shadow@your-file-system.com>