Fix duplicate "Needed By" pointers between changes

Sometimes multiple "Needed By" pointers to the same change were shown
in the web UI, as multiple patch sets of that other change used this
change as an ancestor.  Fix that by taking a distinct set of them.

Change-Id: I6d28937008688d1610f5bab1f121fc83ed20c067
Signed-off-by: Shawn O. Pearce <sop@google.com>
1 file changed