special case check for this situation

special case check for this situation

	; cat >http.go
	package main
	import "http"  // intended the library, not this file
	^D
	; 6g http.go
	; 6g http.go
	http.go:4: export/package mismatch: init
	;

new error:

	http.6:7 http.go:3: cannot import package main

R=ken
OCL=27053
CL=27053