added get_field_default_value() function which obtains default value from the field
(used in store_create_info() & get_schema_column_record() functions)
specifying DEFAULT
This was not specific to datetime. When there is no default value
for a column, and the user inserted DEFAULT, we would write
uninitialized memory to the table.
Now, insist on writing a default value, a zero-ish value, the same
one that comes from inserting NULL into a not-NULL field.
(This is, at best, really strange behavior that comes from allowing
sloppy usage, and serves as a good reason always to run one's server
in a strict SQL mode.)
Moved enabling of warnings to ensure that no warnings are generated
when this test case is executed on a clone where InnoDB is not
activated. This would fail the test case in those clones otherwise.
