the tree can now run the full suite of tests out of the box.
- Migrated most @supported to @fails_on, @fails_on_everything_but, or (last
resort) @unsupported. @fails_on revealed a slew of bogus test skippage,
which was corrected.
- Added @fails_on_everything_but. Yes, the first usage *was*
"fails_on_everything_but('postgres')". How did you guess!
- Migrated @supported in dialect/* to the new test-class attribute __only_on__.
- Test classes can also have __unsupported_on__ and __excluded_on__.
- changed the various "literal" generation functions to use an anonymous
bind parameter. not much changes here except their labels now look
like ":param_1", ":param_2" instead of ":literal"
- from_obj keyword argument to select() can be a scalar or a list.