user query string normalization by pre-parsing with Ferret query parser

user query string normalization by pre-parsing with Ferret query parser
This is a bit of a hack, because it relies on the fact that Ferret query
objects, when converted to string form, are normalized to have +field:text
and -field:text instead of AND, OR, and NOT keywords. Then we can apply
all our string substitutions to just the normalized form.