PHP-1158: Don't log connectTimeoutMS replacement when changing default

https://jira.mongodb.org/browse/PHP-1158
Let's compare to the same code in [1.5.4](https://github.com/mongodb/mongo-php-driver/blob/6fa1d10fd7a64beb34be29bc1c38d0ce727ad05d/mcon/parse.c#L378). Previously, we logged "Replacing..." if the existing value was non-zero and then proceeded to always log "Found option..." and perform the assignment.

In #721, I changed the order of the "Found option..." and "Replacing..." log messages (I believe that's more intuitive), and only did the assignment if the values differed (to avoid a NOP).

With this PR, I now log "Replacing..." only if the previous value is not the default.

And since I can no longer have "Replacing..." and the assignment in the same conditional, I moved it below. I could wrap the assignment in another "if the values differ" conditional, but I opted not (in hindsight, all of the other option routines do assignments regardless).

The edge case Let's compare to the same code in [1.5.4](https://github.com/mongodb/mongo-php-driver/blob/6fa1d10fd7a64beb34be29bc1c38d0ce727ad05d/mcon/parse.c#L378). Previously, we logged "Replacing..." if the existing value was non-zero and then proceeded to always log "Found option..." and perform the assignment.

In #721, I changed the order of the "Found option..." and "Replacing..." log messages (I believe that's more intuitive), and only did the assignment if the values differed (to avoid a NOP).

With this PR, I now log "Replacing..." only if the previous value is not the default.

And since I can no longer have "Replacing..." and the assignment in the same conditional, I moved it below. To be strict, I could wrap the assignment in another "if the values differ" conditional, but I opted not to.

As I mentioned in IRC, we do have an edge case where "Replacing..." probably should be logged but isn't, is if the user cycles through multiple ways of assigning connectTimeoutMS:

 * Process `connectTimeoutMS=0` from query string. We do not log that we're replacing 60000 (the default). Even though 0 would imply "use the default" later in mcon or `io_stream.c`, the parser isn't aware of that. I could also have used 1 here, but just wanted to note this point.
 * Process `timeout=60000` from query string. We log that we're replacing 0.
 * Process `connectTimeoutMS => 0` from the options array. We again do not log that we're replacing a value, because the current value (60000) coincides with the default.

It would be nice if "Replacing..." was logged for that third bullet, but this would require doing something similar to what we have for `MongoCursor::$timeout` or having an extra option to track if `connectTimeoutMS` is ever assigned by the parser, and I don't think either of us want that :)