NUMBERS IN AN 'IN' OF A SELECT (...)

When the range optimizer constructs the SEL_ARG graph from the
predicates, get_mm_leaf() will convert constant values to the 
appropriate type so a field vs constant comparison can be done.
This is done by calling Item::save_in_field_no_warning().

If this conversion is not OK for some reason, get_mm_leaf() will
conclude that the predicate is either always false or always
true. Consider

Q1: EXPLAIN SELECT * FROM t1 WHERE a > value;
 and
Q2: EXPLAIN SELECT * FROM t1 WHERE a > 'value';

where value is a number higher than the maximum value for int
column a. In Q1, get_mm_leaf() finds that the predicate is always
false. In Q2 on the other hand, get_mm_leaf() intreprets the
conversion error from string to int incorrectly and assumes that
the condition is always true to be on the safe side. Due to this,
the range access method is not used for this query.

Before this fix, get_mm_leaf() would only come to the 
conclusion that the range was impossible if both the constant
and the field had an INT type. With this bugfix, quoted numbers
will be treated the same way.