assign the proper result type of Boolean to the result mapping, and
instead would leak column types from within the query into the
result map.  This issue exists in 0.9 and earlier as well, however
has less of an impact in those versions.  In 1.0, due to #918
this becomes a regression in that we now rely upon the result mapping
to be very accurate, else we can assign result-type processors to
the wrong column.   In all versions, this issue also has the effect
that a simple EXISTS will not apply the Boolean type handler, leading
to simple 1/0 values for backends without native boolean instead of
True/False.   The fix includes that an EXISTS columns argument
will be anon-labeled like other column expressions; a similar fix is
implemented for pure-boolean expressions like ``not_(True())``.
fixes #3372

a label that was anonymous, then labeled again with a name, would
fail to be locatable via a textual label.  This situation occurs
naturally when a mapped :func:`.column_property` is given an
explicit label in a query.
fixes #3340

for memoization on a class that uses slots.
- apply many more __slots__.  mem use for nova now at 46% savings

return type is not strictly assumed to be boolean; it now
returns a :class:`.Boolean` subclass called :class:`.MatchType`.
The type will still produce boolean behavior when used in Python
expressions, however the dialect can override its behavior at
result time.  In the case of MySQL, while the MATCH operator
is typically used in a boolean context within an expression,
if one actually queries for the value of a match expression, a
floating point value is returned; this value is not compatible
with SQLAlchemy's C-based boolean processor, so MySQL's result-set
behavior now follows that of the :class:`.Float` type.
A new operator object ``notmatch_op`` is also added to better allow
dialects to define the negation of a match operation.
fixes #3263

anonymous bound parameter names within expressions, to match the
existing use of this value as the key when rendered in an INSERT
or UPDATE statement.   This allows :attr:`.Column.key` to be used
as a "substitute" string to work around a difficult column name
that doesn't translate well into a bound parameter name.   Note that
the paramstyle is configurable on :func:`.create_engine` in any case,
and most DBAPIs today support a named and positional style.
fixes #3245