( [resource link_identifier] )
sybase_close() closes the link to a Sybase
database that's associated with the specified link
If the link identifier isn't specified, the last opened link is
Returns TRUE on success or FALSE on failure.
Note that this isn't usually necessary, as non-persistent
open links are automatically closed at the end of the script's
sybase_close() will not close persistent links
generated by sybase_pconnect().