updates for iOS6
Method swizzling works & tested

Images dont re-load when returning from background now
Shifts decode/set into a cancelable operation

the image setting code can be cancelled in-flight which should offer
"smoother" operation on older devices.
removed unnecessary logging
grrr background decode queue doesn't work
image decode operation is now working!
clean ups
Merge branch 'master' of https://github.com/tonymillion/TMDiskCache