Fixed bug in MySQLdb dialect and variants such as PyMySQL where an
additional "unicode returns" check upon connection makes explicit use of
the "utf8" character set, which in MySQL 8.0 emits a warning that utf8mb4
should be used.  This is now replaced with a utf8mb4 equivalent.
Documentation is also updated for the MySQL dialect to specify utf8mb4 in
all examples.  Additional changes have been made to the test suite to use
utf8mb3 charsets and databases (there seem to be collation issues in some
edge cases with utf8mb4), and to support configuration default changes made
in MySQL 8.0 such as explicit_defaults_for_timestamp as well as new errors
raised for invalid MyISAM indexes.

Change-Id: Ib596ea7de4f69f976872a33bffa4c902d17dea25
Fixes: #4283
Fixes: #4192

Fixed INSERT FROM SELECT with CTEs for the Oracle and MySQL dialects, where
the CTE was being placed above the entire statement as is typical with
other databases, however Oracle and MariaDB 10.2 wants the CTE underneath
the "INSERT" segment. Note that the Oracle and MySQL dialects don't yet
work when a CTE is applied to a subquery inside of an UPDATE or DELETE
statement, as the CTE is still applied to the top rather than inside the
subquery.

Also adds test suite support CTEs against backends.

Change-Id: I8ac337104d5c546dd4f0cd305632ffb56ac8bf90
Fixes: #4275
Fixes: #4230

Fixed a 1.2 regression caused by :ticket:`4061` where the SQL Server
"BIT" type would be considered to be "native boolean".  The goal here
was to avoid creating a CHECK constraint on the column, however the bigger
issue is that the BIT value does not behave like a true/false constant
and cannot be interpreted as a standalone expression, e.g.
"WHERE <column>".   The SQL Server dialect now goes back to being
non-native boolean, but with an extra flag that still avoids creating
the CHECK constraint.

Change-Id: I4765d2a2a00b0d14f50282603cc4d48d4739dac1
Fixes: #4250

 * Causes intermittent failure against Greenplum cluster
 * Tested using Greenplum dialact:
     https://github.com/PlaidCloud/sqlalchemy-greenplum

Change-Id: I6387e98f17a3667612fdaaadb27a08f79ec46398
Pull-request: https://github.com/zzzeek/sqlalchemy/pull/440

Fixed 1.2 regression caused by :ticket:`4060` where the query used to
reflect SQL Server cross-schema foreign keys was limiting the criteria
incorrectly.

Additionally, added some rework of the inter-schema reflection tests
so that MySQL, MSSQL can be included, breaking out some of the
Postgresql-specific behaviors into separate requirements.

Fixes: #4234
Change-Id: I20c8e70707075f1767b79127c2c27d4b313c6515

Fixed issue where the compilation of an INSERT statement with the
"literal_binds" option that also uses an explicit sequence and "inline"
generation, as on Postgresql and Oracle, would fail to accommodate the
extra keyword argument within the sequence processing routine.

Change-Id: Ibdab7d340aea7429a210c9535ccf1a3e85f074fb
Fixes: #4231

The ON DELETE options for foreign keys are now part of
Oracle reflection.  Oracle does not support ON UPDATE
cascades.  Pull request courtesy Miroslav Shubernetskiy.

Change-Id: I135cd6cd3436354a86b2c1e1437c3785c38eed26
Pull-request: https://github.com/zzzeek/sqlalchemy/pull/418

This is the only way I could get this test pass on informix, basically I strip every whitespace.
The sql text as recorded in informix is:
```
((a > 1 ) AND (a < 5 ) )
((a = 1 ) OR ((a > 2 ) AND (a <5 ) ) )
```
Yes, this is absolutely bonkers, but that is what I get :(

Change-Id: I936e860f2b75b521e5560c05c452dbe72f0d3812
Pull-request: https://github.com/zzzeek/sqlalchemy/pull/413