Make OpenAFS 1.6.18.3

Make OpenAFS 1.6.18.3

Update configure version strings for 1.6.18.2. Note that macos kext
can be of form XXXX.YY[.ZZ[(d|a|b|fc)NNN]] where d dev, a alpha,
b beta, f final candidate so we have no way to represent 1.6.18.3.
Switch to 1.6.19 dev 3 for macos.

Change-Id: I30fed9209c101d290b8bd182c8f90efd83062caf
Reviewed-on: https://gerrit.openafs.org/12356
Reviewed-by: Mark Vitale <mvitale@sinenomine.net>
Reviewed-by: Stephan Wiesand <stephan.wiesand@desy.de>
Tested-by: Stephan Wiesand <stephan.wiesand@desy.de>