Bug # 17894 - Comparison with "less than" operator fails with range partition

The problem here was that on queries such as < 3, the range given is NULL < n < 3.
The null part works correctly where the null value is stored in rec[0] and the
field is marked as being null.  However, when the 3 is processed, the 3 is places
on rec[0] but the null flag is left uncleared.

partition_range.result:
  Results block for bug #17894
partition_range.test:
  Test block for bug #17894
partition_list.result:
  Results block for bug #17173
partition_list.test:
  Test block for bug #17173
opt_range.cc:
  call set_notnull to clear any null flag that may have been set