Arguments such as cipher, kdf_iter, cipher_page_size and
cipher_use_hmac may (always?) require quotes within the
PRAGMA directive.

Change-Id: I2c808f34e1c44f0593b72b304e170e4af0a6035a
Pull-request: https://github.com/zzzeek/sqlalchemy/pull/319

Fixed regression caused by the fix in :ticket:`3807` (version 1.1.0)
where we ensured that the tablename was qualified in the WHERE clause
of the DO UPDATE portion of PostgreSQL's ON CONFLICT, however you
*cannot* put the table name in the  WHERE clause in the actual ON
CONFLICT itself.   This was an incorrect assumption, so that portion
of the change in :ticket:`3807` is rolled back.

Change-Id: I442d8629496a8e405b54711cfcf487761810ae8a
Fixes: #3846
Fixes: #3807

Options like uselist and backref can be determined from
within _register_attribute based on parent_property
given; move this logic inside so that individual strategies
have less responsibility.  Also don't require that
_register_attribute consider the "strategy" itself
at all; it would be better if we could no longer require
that Joined/Subquery/etc loaders call upon the "lazy" strategy
in order to initialize attribute instrumentation and
this could be done more generically.

Fixes long-standing bug where the "noload" relationship loading
strategy would cause backrefs and/or back_populates options to be
ignored.   There is concern that some application that uses
"noload" might be surprised at a back-populating attribute
appearing suddenly, which may have side effects.  However,
"noload" itself must be extremely seldom used since as a
strategy, it already disables loading, population of attributes
is the only behavior that is even supported, so that this issue has existed
for at least through 0.7 four years ago without ever being
reported indicates extremely low use of this option.

Change-Id: Icffb9c83ac5782b76ce882ed1df4361a1efbfba3
Fixes: #3845

MySQL's native ENUM type supports any non-valid value being sent, and
in response will return a blank string.  A hardcoded rule to check for
"is returning the blank string" has been added to the  MySQL
implementation for ENUM so that this blank string is returned to the
application rather than being rejected as a non-valid value.  Note that
if your MySQL enum is linking values to objects, you still get the
blank string back.

Change-Id: I61f85c20293a48b0c11a31f2a19f6756c206bd20
Fixes: #3841

Change-Id: I6545ebfeeee103cac133d0b8270a860cba2d2996

Fixed regression caused by :ticket:`2677` whereby calling
:meth:`.Session.delete` on an object that was already flushed as
deleted in that session would fail to set up the object in the
identity map (or reject the object), causing flush errors as the
object were in a state not accommodated by the unit of work.
The pre-1.1 behavior in this case has been restored, which is that
the object is put back into the identity map so that the DELETE
statement will be attempted again, which emits a warning that the number
of expected rows was not matched (unless the row were restored outside
of the session).

Change-Id: I9a8871f82cb1ebe67a7ad54d888d5ee835a9a40a
Fixes: #3839