Add a wrapper around the PAK-file DDC backend which can compress cache entries. Big reduction in the size of the DDC pak file, and seems to add negligable amount (measured average < 0.5s) to startup time. For UE-8823.
[CL 2449854 by Matthew Griffin in Main branch]
Fix for building engine DDC on Mac; suspect that lock is due to recursion in FDerivedDataBackend::Get(), due to recursion through WaitForQuiescence. Instead of appending existing cache on startup, append it on shutdown if a command line parameter is present instead.
[CL 2426046 by Ben Marsh in Main branch]
Add a parameter to the pak file backend to merge DDC with an existing cache, and include DDC for MobileStarterContent and templates in Rocket build.
#codereview Matthew.Griffin
[CL 2425921 by Ben Marsh in Main branch]
Unshelved this merge from Stephan and then completed the merge with additional fixes and testing.
Hand fixed some WorldExp compile issues due to changes to OnPaint() signature.
#Integration
[CL 2245992 by Daniel Broder in Main branch]
There was a bug in setting affinity of a thread that assumed affinity from lookup table with key being a thread name. When names was appended with consecutive numbers (e.g. "RenderingThread 1") the mechanism failed. Refactored this to use special static consts describing affinity override'able by different platforms for different affinity types + possibility of setting affinity per thread.
#codereview Jaroslaw.Surowiec
[CL 2070197 by Jaroslaw Palczynski in Main branch]
#proj core
#branch UE4
#summary Remove all bAutoDeleteSelf and bAutoDeleteRunnable usage from the runnable.
#codereview Robert.Manuszewski
[CL 2070165 by Mikolaj Sieluzycki in Main branch]
