Couple summarize fixes

The correct value for prev_revision form attribute is the active
revision id. The naming is based on the thought that this is
the prev_revision to the revision you are trying to create.

Additionally submitted content was not being repopulated on failed
submission, this was due to the field being named summary but the
template looking for a content variable.

Change-Id: Ibab85b22941fbcefaa41e1b84898c419699731d4
Merge "Couple summarize fixes" into frontend-rewrite