correctly handle doc urls containing "//"

A doc generation bug resulted in Google indexing links containing "//", which cause
problems with linked content (images/css/etc).  This rule generates a 301 redirect
for these links.

Change-Id: Iff1e73e0f3db80c11a56a08abd67dd6c050c1aa1
Partial-bug: 1288513
Merge "correctly handle doc urls containing "//""