Very few of the compiler regression tests include a comment
saying waht they do. Many are obvious, some are anything but.
I've started with a-c in the top directory. More will follow once
we agree on the approach, correctness, and thoroughness here.
zerodivide.go sneaked in too.
R=rsc, r
CC=golang-dev
https://golang.org/cl/5656100
There is no semantic change here, just better errors.
If a function says it takes a byte, and you pass it an int,
the compiler error now says that you need a byte, not
that you need a uint8.
Groundwork for rune.
R=ken2
CC=golang-dev
https://golang.org/cl/5300042
