Add double slash after Bwana.app's man protocol

Safari 6's unified location and search bar can no longer tell the
difference between a protocol and a colon search.

modules/osx/functions/manb

@@ -9,7 +9,7 @@ function manb {
   local page
   if (( $# > 0 )); then
     for page in "$@"; do
-      open "man:$page" 2>/dev/null
+      open "man://$page" 2>/dev/null
       if (( $? != 0 )); then
         print "$0: Bwana is not installed" >&2
         break