Fixed issue where a default of CURRENT_TIMESTAMP would not
properly reflect when using MariaDB 10.2, as a parenthesis
is now added to the expression that wasn't being matched.

Change-Id: I8666d61814e8145ca12cbecad94019b44af868e3

Change-Id: Ic5eb90049358935995721765b2239cf91144895a

Fixed bug where an index reflected under Oracle with an expression like
"column DESC" would not be returned, if the table also had no primary
key, as a result of logic that attempts to filter out the
index implicitly added by Oracle onto the primary key columns.

Reworked the "filter out the primary key index" logic in oracle
get_indexes() to be clearer.

This changeset also adds an internal check to ColumnCollection
to accomodate for the case of a column being added twice,
as well as adding a private _table argument to Index such that
reflection can specify the Table explicitly.  The _table
argument can become part of public API in a later revision
or release if needed.

Change-Id: I745711e03b3e450b7f31185fc70e10d3823063fa
Fixes: #4042

Enabled UUID support for the pg8000 driver, which supports native Python
uuid round trips for this datatype.  Arrays of UUID are still not supported,
however.

Change-Id: I44ca323c5d9f2cd87327210233bc36a3556eb050
Fixes: #4016

Fixed bug where the pg8000 driver would fail if using
:meth:`.MetaData.reflect` with a schema name, since the schema name would
be sent as a "quoted_name" object that's a string subclass, which pg8000
doesn't recognize.   The quoted_name type is added to pg8000's
py_types collection on connect.

Change-Id: Id0f838320cb66563685e094e4eae2d5116100d27
Fixes: #4041

Change-Id: Icc742bbeecdb7448ce84caccd63e086af16e81c1
Fixes: #4026

Change-Id: Ied786e8f9ad78f524be03a382d002dada7dd218b