Disable antijoin transformation if this is:
- NOT EXISTS, or <constant> NOT IN,
- and the subquery is not correlated.
Otherwise we got this type of plan:
nested loop antijoin
   -> outer
   -> inner
and we would read each row of "outer", only to find, every time, that
there is a row in "inner" and that we should not emit the row of "outer".
Instead, we evaluate the subquery during optimization, leading to an always
true or false condition.
This does not cancel Steinar's patch for the same bug report; however it
makes "case 2" (see his commit comment) apply only to antijoin coming from
LEFT JOIN, as antijoin coming from NOT EXISTS will not reach the executor
anymore, due to the present patch.

Approved by: Roy Lyseng <roy.lyseng@oracle.com>

Change-Id: I59a887456a56039a6b1480b3ec8f7ac188d1ce58