kvo.m without autorelease

Save yourself an autorelease.  
I haven't written non-ARC code in a long time but retain, release, assign is still comes naturally :) good old times.

Thanks for sharing the snippets. Some are quite trivial, but it's always inspiring to have a peek behind the curtain.
KVO ala ARC
Merge pull request #5 from stigi/patch-1

kvo.m without autorelease