Flush ContentState during FeatureType DELETE (GEOS-6616)

Restore DELETE operations ability to clear cached FeatureType information (GEOS-6616)

For details see: https://jira.codehaus.org/browse/GEOS-6616
Merge pull request #679 from jodygarnett/GEOS-6616

Flush ContentState during FeatureType DELETE (GEOS-6616)

Patch limited flushing content state (or falling back to datastore dispose) during DELETE operation

Resetting datastore cached attributes during PUSH creation of a FeatureType can be a new feature for 2.7.x.