upgrade to geogit 0.9-SNAPSHOT
geogit-GWC integration: truncate tiles affected by remote pushes.

The org.geogit.gwc package contains a "claspath" hook that catches
UpdateRef command calls, figures out which geogit datastores and
gwc tile layers would be affected by the ref update, for each
tile layer computes a "minimal bounds" geometry, and uses gwc truncate
tasks on each affected layer using the minimal bounds geometry as
a mask in order to adjust the truncated tiles to the regions affected
by the change to the geogit repository as much as possible.
comment out call to method not existent in gwc 1.5.x