Unexports runtime.MemStats and rename MemStatsType to MemStats.
The new accessor requires passing a pointer to a user-allocated
MemStats structure.
Fixes#2572.
R=bradfitz, rsc, bradfitz, gustavo
CC=golang-dev, remy
https://golang.org/cl/5616072
* adds pass 3 to dequeue from channels eagerly
various other cleanup/churn:
* use switch on cas->send in each pass to
factor out common code.
* longer goto labels, commented at target
* be more agressive about can't happen:
throw instead of print + cope.
* use "select" instead of "selectgo" in errors
* use printf for debug prints when possible
R=ken2, ken3
CC=golang-dev, r
https://golang.org/cl/875041
