buildhistory: remove duplicate entries from dot graph

buildhistory: remove duplicate entries from dot graph

There are various conditions that lead to duplicate entries in the dot graph which need to get fixed, but this patch is a catchall. A previous attempt to address this only works on rpm which gives a \n seperated output, opkg doesn't.

Another benefit is that the sort order is now know, leading to less spurious diffs in buildhistory commits.

(From OE-Core rev: 479ae1e9b74aa2f04fb5da2f3541c3de0aa9de87)

Signed-off-by: Koen Kooi <koen@dominion.thruhere.net>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>