BUG-13 delete loan fails with foreign key issues, all fixed

BUGs

@@ -3,7 +3,6 @@
 ### DB/back-end
 BUG-2:		series does not deal with calcd_rating... 
 			- (on edit could, recalc as a catch-all, and obviously if we change a single book's rating, we should re-calc)
-BUG-13:		deleting loan fails with book_loan_link data still existing
 
 ### UI not updating after DB change:
 BUG-3:		alter a condition, covertype, etc. and its not in drop-down list (even though db look via index is correct, e.g books.html shows updated covertype)

loan.py

@@ -87,6 +87,8 @@ def loan(id):
         try:
             if 'delete' in request.form:
                 st.SetMessage("Successfully deleted (id={}, who={} {})".format( loan.id, loan.firstnames, loan.surname ) )
+                # fall back to direct sql because loan.py is imported before Book_Loan_Link exists
+                db.engine.execute("delete from book_loan_link where loan_id = {}".format( loan.id ))
                 loan = Loan.query.filter(Loan.id==id).delete()
             if 'submit' in request.form:
                 st.SetMessage("Successfully Updated Loan (id={})".format(id) )