allow undef set to store NULLs
update test as we can set null now
fallback to default value if we are setting undef to a not-null field
test null set when the old value is already null
test warning when setting a feild from null to not-null
return error directly if set undef to a NOT NULL field which lacks DEFAULT
20set_edge_cases for more edge case tests

test of setting undef/empty string to a NOT NULL field without DEFAULT
return way to get old behaviour
update changelog
Number is reserved keyword in Oracle
A more descriptive error message when trying to null a non-nullable field
Update tests for 3ed462f
Merge branch 'set-undef-fix'

Conflicts:
	Changes