gc: allow ~ in import paths Windows has paths like C:/Users/ADMIN~1. Also, it so happens that go/parser allows ~ in import paths. So does the spec. Fixes the build too.
gc: allow ~ in import paths
Windows has paths like C:/Users/ADMIN~1. Also, it so happens
that go/parser allows ~ in import paths. So does the spec.
Fixes the build too.

R=golang-dev, dsymonds
CC=golang-dev
http://codereview.appspot.com/5777073

apparentlymart/golang,apparentlymart/golang,pombredanne/go-deleteme,tv42/old-go,gnanderson/go,gnanderson/go,apparentlymart/golang,gnanderson/go,dsriram/golang,pombredanne/go-deleteme,tv42/old-go,gnanderson/go,gnanderson/go,dsriram/golang,tv42/old-go,tv42/old-go,gnanderson/go,dsriram/golang,pombredanne/go-deleteme,pombredanne/go-deleteme,apparentlymart/golang,tv42/old-go,dsriram/golang,apparentlymart/golang,pombredanne/go-deleteme,pombredanne/go-deleteme,gnanderson/go,tv42/old-go,tv42/old-go,dsriram/golang,apparentlymart/golang,dsriram/golang,pombredanne/go-deleteme,apparentlymart/golang,dsriram/golang