LP#1516707: Phrase search ignores CD modifiers

LP#1516707: Phrase search ignores CD modifiers

Because phrases are subqueries, we need to look at the top of the parse tree
when looking for modifiers for cover density.  This is because modifers are
normally only allowed at the top of the parse tree (or in the floating sub-
query).  We do that by asking the plan's QueryParse for it's reference to its
parse_tree member, which is always the top of the parse tree in QP.

Included in this commit is a small change to the QP testing script to
facilitate testing of this fix.

Signed-off-by: Mike Rylander <mrylander@gmail.com>
Signed-off-by: Kathy Lussier <klussier@masslnc.org>