move constant index checking to front end x[2:1] is a compile-time error now too R=ken2 CC=golang-dev https://golang.org/cl/1848056
R=iant, ken2, r, r2, ken3 CC=golang-dev https://golang.org/cl/1686044
1. Fix bug in GOMAXPROCS when trying to cut number of procs Race could happen on any system but was manifesting only on Xen hosted Linux. 2. Fix recover on ARM, where FP != caller SP. R=r CC=golang-dev https://golang.org/cl/880043
R=ken2, r CC=golang-dev https://golang.org/cl/871042
