notmuch dump: Fix the sorting of results.

To properly support sorting in notmuch_query we know use an
Enquire object. We also throw in a QueryParser too, so we're
really close to being able to support arbitrary full-text
searches.

I took a look at the supported QueryParser syntax and chose
a set of flags for everything I like, (such as supporting
Boolean operators in either case ("AND" or "and"), supporting
phrase searching, supporting + and - to include/preclude terms,
and supporting a trailing * on any term as a wildcard).