Add Python3 special methods for division to SQLExpression
Add Python3 special methods for division to SQLExpression

Adds __truediv__ and __floordiv__ (and reciprocals) to better support using
SQLExpression objects in Pythonn3.

Note that __floordiv__ is NOT equivalent to SQL's 'DIV' operator, so the
SQL FLOOR function is used in combination with the / operator.

Should be backwards-compatible with Python2.

sqlobject/sqlobject,drnlm/sqlobject,sqlobject/sqlobject,drnlm/sqlobject