Correct SQLAnywhere driver default port to 2638

References:
SQLA16 - http://dcx.sybase.com/index.html#sa160/en/dbadmin/serverport-network-conparm.html
SQLA12 - http://infocenter.sybase.com/help/index.jsp?topic=/com.sybase.help.sqlanywhere.11.0.1/dbadmin_en11/serverport-network-conparm.html
Merge pull request #620 from Slashbunny/fix-sqlanywhere-default-port

Correct SQL Anywhere driver default port to 2638