go/loader: don't treat unsafe specially wrt vendoring

The loader treats GOROOT's "unsafe" package specially,
with no source files and a Package of types.Unsafe.

Tested on Go 1.4.1, 1.5, and ~1.6 (tip).

Fixes issue #13882

Change-Id: I86c4e394665d86a50ec3852d6d702f0e9c5d2276
Reviewed-on: https://go-review.googlesource.com/18457
Reviewed-by: Robert Griesemer <gri@golang.org>
diff --git a/go/loader/util.go b/go/loader/util.go
index 4e01462..7f38dd7 100644
--- a/go/loader/util.go
+++ b/go/loader/util.go
@@ -103,8 +103,8 @@
 					if err != nil {
 						continue // quietly ignore the error
 					}
-					if path == "C" || path == "unsafe" {
-						continue // skip pseudo packages
+					if path == "C" {
+						continue // skip pseudopackage
 					}
 					imports[path] = true
 				}