cmd/cgo, cmd/go: support including C++ code with cgo (CL 8248043).
cmd/go: test coverage (CL 10413044).
+container/heap: added Fix (CL 12265043).
+container/list: added MoveBefore and MoveAfter (CL 12021044).
crypto/md5: Sum function to simplify hashing (CL10624044).
crypto/sha1: Sum function to simplify hashing (CL 10571043).
crypto/sha256: Sum256 and Sum224 functions to simplify hashing (CL 10629043).
image/gif: added Encode and EncodeAll (CL 10896043).
io: Copy prioritizes WriterTo over ReaderFrom (CL 9462044).
net: new build tag netgo for building a pure Go net package (CL 7100050).
+runtime: allow SetFinalizer with a func(interface{}) (CL 11858043).
runtime: preemption of goroutines at function entry (CL 12371043).
sort: new Stable function provides stable sort (CL 9612044).
syscall: implemented Sendfile for Darwin, added Syscall9 for Darwin/amd64 (CL 10980043).