mt local write stream: shortcut fast-forward
mt local write stream: shortcut fast-forward

Don't err if expected local head mismatches the current local head if
one of the parents of the new version references the current local
head.

Netsend/persdb,Netsend/PerspectiveDB,Netsend/PerspectiveDB,Netsend/persdb,Netsend/PerspectiveDB,Netsend/persdb