Add Mac OS X deployment target
Add 64bit support for the library
Fix type issue
Only build the active architecture for debug
Get test target building
Add flags for the test target
Add test for threaded access to the context

This test doesn't always cause a crash, it happens usually once in every three times.
Add a fix for threaded access to the context

Fixes the case when the context is accessed from two (or more) threads for the first time, causing the setup process to fire and collide when setting up the persistent store coordinator.
Remove 64-bit support until we can target iOS 5 and arm64 together
Remove arm64 until we can target less than iOS 7
Combine HiDPI images on the Mac demo target