4 - better GC for IORef/IOArray and lots of threads
5 - loosen rules on instance decls
12 - -split-objs now works with --make and Cabal
13 - relaxed dependency analysis (with -fglasgow-exts)
14 - old syntax for FFI declarations is no longer accepted
20 Internals/Source tree:
22 - unknown calls take args in registers, if available
23 - x86_64: more argument regs
26 - source tree flattened