Convert type casts

[ahinz]

Right now we're doing: (sql.Rows*)dbc however we may want to use "type assertions" instead dbc.(sql.Rows*) http://golang.org/ref/spec#Type_assertions

[steventlamb]

When I try this I get the following error:

Godeps/_workspace/src/github.com/azavea/ecobenefits/eco/db.go:25: invalid type assertion: dbr.(*sql.Rows) (non-interface type
 *DBRow on left) 

Looks like it's only for interfaces:
http://stackoverflow.com/questions/18691927/go-named-type-assertions-and-conversions