Fix double encoded characters in gitweb -> gitblit forwards

The combination of 'AllowEncodedSlashes On' and [B] caused '/' in
project names to be translated into '%252f' ('/' encoded twice)
instead of '%2f' ('/' encoded once). As the RewriteRule's
replacement's backreferences get escaped through [B], and the
remaining parts are plain harmless strings, we turn off encoding of
the rewritten URL.

Bug: 41961
Change-Id: I949fc00341d08147ad72cdb860526a7dbcd9dc83