Scan for available serial com ports

The function uses a simple workaround (as there is no documented way) to first scan for all available ports and returns only those which are ready for use. As the procedure involves testing each port individually it takes a few seconds (about the same a Terminal/Hyperterminal takes on port rescan).

Request in the comments section for any additional features like error message encountered for each port, etc and I'll consider revising.

Cheers,
cK.