Prevent the pool from closing sockets on connections that are actively in use
by other threads when the master address changes. Connections returned to the
pool that are still connected to the old master will be disconnected
gracefully.

Fixes #1345

Fixed #1339

The lock does not need to be held while waiting for the socket to
establish and validate the TCP connection.

flake8 catches a wider net of mistakes than pycodestyle and is more
commonly used by the larger community. For example, it catches unused
imports, a few of which existed. These have since been removed.

Two "noqa" comments were added. One ignores the _compat.py file as it
has a large amount of Python version specific code. The second is in
utils.py which intentionally does not use an import.

Calling str() on a bytes object can result in a BytesWarning being
emitted and usually indicates a mixup between byte and string handling.

Now, in the event of an invalid RESP response, use the repr value of the
raw response in the exception message.

Can further simplify the bytes/str handling by comparing the first byte
as a bytes object instead of converting it to str. The bytes literal is
available on all supported Pythons. This removes the need for the
compatibility function, byte_to_chr().

Use the "as" keyword to capture the exception in a variable instead of
sys.exc_info().

Re-raise exception with the bare "raise" syntax.

Avoid "# noqa: E722" by catching BaseException, which includes all
exceptions including SystemExit.

This allows memoryview instances to be passed to Redis command args that
expect strings or bytes. The memoryview instance is sent directly to
the socket such that there are zero copies made of the underlying data
during command packing.

Fixes #1265
Fixes #1285