Use reflection-driven field accesses under GopherJS.
Like App Engine, GopherJS does not support unsafe.
This change adds a 'js' build tag (set by GopherJS)
alongside the existing 'appengine' tags.
Fixes #154.
diff --git a/proto/pointer_unsafe.go b/proto/pointer_unsafe.go
index e9be0fe..ceece77 100644
--- a/proto/pointer_unsafe.go
+++ b/proto/pointer_unsafe.go
@@ -29,7 +29,7 @@
// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
-// +build !appengine
+// +build !appengine,!js
// This file contains the implementation of the proto field accesses using package unsafe.