Update khash to 0.2.8
Add experimental support for pf on Mac OS X

Support pf rdr on Mac OS X 10.7, 10.8 and 10.9 by including the missing
Apple headers in the source tree and enable private Apple code.  Since
we are using an interface marked private by Apple, this code is very
experimental.

Issue:		#15
Reported by:	Amit Chowdhary