Item12717: Bump version from release branch

Increment trunk from 2.60 to 2.70 so the release branch has some room
for additional release if needed.  Add Item12717 to the change log.

git-svn-id: http://svn.foswiki.org/trunk@17461 0b4bb1d4-4e5a-0410-9cc4-b2b747904278