The heuristics options tries to the default full copytracing algorithm if both
the source and destination branches contains of non-public changesets only. But
this can be slow in cases when we have a lot of drafts.
This patch adds a new config option experimental.copytrace.sourcecommitlimit
which defaults to 100. This value will be the limit of number of drafts from c1
to base. Incase there are more changesets even though they are draft, the
heuristics algorithm will be used.
Oops. repo isn't passed to this function.
Write tests?