such as :meth:`.Query.union` now handle the case where the embedded
SELECT statements need to be parenthesized due to the fact that they
include LIMIT, OFFSET and/or ORDER BY.   These queries **do not work
on SQLite**, and will fail on that backend as they did before, but
should now work on all other backends.
fixes #2528

- test for .cast() method has no good place now except for
test_cast in test_compiler.py

by the ORM :class:`.Query` object (part of the performance
enhancements of :ticket:`3175`) would not raise the "this result
does not return rows" exception in the case where the driver
(typically MySQL) fails to generate cursor.description correctly;
an AttributeError against NoneType would be raised instead.
fixes #3481

un-adjusted internal symbol names for "anonymous" labels, which
are the "foo_1" types of labels we see generated for SQL functions
without labels and similar.  This was a side effect of the
performance enhancements implemented as part of references #918.
fixes #3483

in conjunction with :func:`.and_` or :func:`.or_` would fail
with an AttributeError.
fixes #3490

of :class:`.FunctionElement` or other column element that incorrectly
states 'None' or any other invalid object as the ``.type``
attribute will report this exception instead of recursion overflow.
fixes #3485