assisting with alembic installations that have upgraded and are dealing with
PG index/unique constraint reflection.

Inspection API already supports reflection of table
indexes information and those also include unique
constraints (at least for PostgreSQL and MySQL).
But it could be actually useful to distinguish between
indexes and plain unique constraints (though both are
implemented in the same way internally in RDBMS).

This change adds a new method to Inspection API - get_unique_constraints()
and implements it for SQLite, PostgreSQL and MySQL dialects.

in-python only cols

of the incoming :class:`.Column` would prevent primary key constraints,
indexes, and foreign key constraints from being correctly reflected.
Also in 0.8.3. [ticket:2811]

Conflicts:
	doc/build/changelog/changelog_09.rst

- rewrite --dropfirst to be more industrial strength, includes views
- fix order_by="foreign_key" to maintain the same ordering as
metadata.sorted_tables.   Not ideal that this was the other way throughout
0.7 but this is still a little-used method, in contrast to metadata.sorted_tables.

convert non-string values to string, to accommodate
old SQLite versions that don't deliver
default info as a string.  [ticket:2265]
- factor sqlite column reflection to be like we did for postgresql,
in a separate method.

- struggle with Operators class autodoc