Handling of connect_timeout parameter has changed, needs further improvements

[joerivanruth]

Before pymonetdb 1.8.0, the value of connection_timeout could be one of:

• -1 (the default), to use the Python-wide default timeout,
• None, to block indefinitely,
• 0, to enable non-blocking mode on the socket,
• >0, to set a timeout.

All negative values except -1 yielded an error message.

Note however that pymonetdb was not designed for use with non-blocking sockets. This means setting it to zero, either directly or using socket.setdefaulttimeout(), has never worked.

In 1.8.0, the behaviour was changed in a not well thought out manner. The default changed to 0 and the values 0 and None both meant "use the system default". Other values, including -1 were passed as-is to socket.settimeout(). However, that function does not accept negative values.

It turns out some users explicitly pass connection_timeout=-1. This now fails, which is undesirable. However, the old behaviour is also suboptimal because value 0 is unusable. It makes more sense to interpret connection_timeout=0 as an explicit request for blocking without timeout.

The following table lists the original, the modified and the desired behaviour:

	1.7.1	1.8.1	DESIRED
unspecified	sysdefault	sysdefault	sysdefault but not non-blocking
-1	sysdefault	error	sysdefault but not non-blocking
other negative	error	error	error
0	non-blocking (broken)	sysdefault	blocking
>0	timeout	timeout	timeout

[joerivanruth]

Tests have been added, issue can be now be closed.