go.tools/cmd/gotype: use go/types identifier resolution

R=adonovan
CC=golang-dev
https://golang.org/cl/14146043

cmd/gotype/doc.go

@@ -59,5 +59,3 @@ To verify the output of a pipe:
 
 */
 package main
-
-// BUG(gri): At the moment, only single-file scope analysis is performed.

cmd/gotype/gotype.go

@@ -74,7 +74,7 @@ func parse(fset *token.FileSet, filename string, src []byte) *ast.File {
 	}
 
 	// parse entire file
-	mode := parser.DeclarationErrors
+	var mode parser.Mode
 	if *allErrors {
 		mode |= parser.AllErrors
 	}