Previously, it was impossible to have a Table that has
None for a schema name when the "schema" parameter on
MetaData was set.  A new symbol sqlalchemy.schema.BLANK_SCHEMA
is added which indicates that the schema name should unconditionally
be set to None.  In particular, this value must be passed within
cross-schema foreign key reflection, so that a Table which
is in the "default" schema can be represented properly.

Fixes: #3716
Change-Id: I3d24f99c22cded206c5379fd32a225e74edb7a8e

Change-Id: I1873dc22c233b5c3585eb7a203bc2352c7cfdbef

Fixed bug in "evaluate" strategy of :meth:`.Query.update` and
:meth:`.Query.delete` which would fail to accommodate a bound
parameter with a "callable" value, as which occurs when filtering
by a many-to-one equality expression along a relationship.

Change-Id: I47758d3f5d8b9ea1a07e23166780d5f3c32b17f1
Fixes: #3700

Change-Id: Idcd77a570b19f1b022a74d67fa8253d922dadc67

cx_Oracle connection parameters user, password and dsn must be
either a string or NULL.  When they are passed a Python None object,
"TypeError: expecting string, unicode or buffer object" is raised.

Fixes: #3705

Change-Id: I8da5d8a227ca12c9bf17a6127460e413841951fb
Pull-request: https://github.com/zzzeek/sqlalchemy/pull/271

This is another psycopg2 error message representing an
unusable connection.

Fixes #3715
Change-Id: Ida6e212963e9c7336bf2944e7ef928619ac3a0e7
Pull-request: https://bitbucket.org/zzzeek/sqlalchemy/pull-requests/85