compiler: reject NOT operator on integer types.
compiler: reject NOT operator on integer types.

The Go specification only accepts the NOT operator on boolean
types.

Fixes #10.

R=iant, gofrontend-dev
CC=gofrontend-dev, remy
https://golang.org/cl/6192053

qskycolor/gofrontend,qskycolor/gofrontend,qskycolor/gofrontend,qskycolor/gofrontend,anlhord/gofrontend,golang/gofrontend,golang/gofrontend,anlhord/gofrontend,anlhord/gofrontend,qskycolor/gofrontend,qskycolor/gofrontend,anlhord/gofrontend,golang/gofrontend,anlhord/gofrontend,golang/gofrontend,anlhord/gofrontend,qskycolor/gofrontend,anlhord/gofrontend