If there is a closed attribute on the connection and
it is true, return true. Implements a todo in the code
and helps in one specific disconnect case where it previously
did not match because the error message was "unknown error".

Found using: https://github.com/intgr/topy

it for DELETE would fail to target the correct row for DELETE.
Then to compound matters, basic "number of rows matched" checks were
not being performed.  Both issues are fixed, however note that the
"rows matched" check requires so-called "sane multi-row count"
functionality; the DBAPI's executemany() method must count up the
rows matched by individual statements and SQLAlchemy's dialect must
mark this feature as supported, currently applies to some mysql dialects,
psycopg2, sqlite only. fixes #3006
- Enabled "sane multi-row count" checking for the psycopg2 DBAPI, as
this seems to be supported as of psycopg2 2.0.9.

enhancements where index reflection on Postgresql versions specific
to only the 8.1, 8.2 series again
broke, surrounding the ever problematic int2vector type.  While
int2vector supports array operations as of 8.1, apparently it only
supports CAST to a varchar as of 8.3.
fix #3000

"could not send data to server", which complements the existing
"could not receive data from server" and has been observed by users,
fixes #2936

(pre 8.1) versions of Postgresql, and potentially other PG engines
such as Redshift (assuming Redshift reports the version as < 8.1).
The query for "indexes" as well as "primary keys" relies upon inspecting
a so-called "int2vector" datatype, which refuses to coerce to an array
prior to 8.1 causing failures regarding the "ANY()" operator used
in the query.  Extensive googling has located the very hacky, but
recommended-by-PG-core-developer query to use when PG version < 8.1
is in use, so index and primary key constraint reflection now work
on these versions.

python_type for ARRAY (PGArray)

hstore extension. #2959

query for  "show standard_conforming_strings"; as this variable was
added as of PG 8.2, we skip the query for PG versions older than
that as well as for backends like Redshift. #2946