Bug 786347 - Fix <a ping> implementation to follow spec r=bz

From ecd12f2127c5b21e78fdb937e8feb7de1da53023 Mon Sep 17 00:00:00 2001
Bug 786347 - Tests for <a ping> implementation r=bz

From 0023364806ae433e55d42a915a9d47e2f18df558 Mon Sep 17 00:00:00 2001