*
* \param \ra string of the form receiver_name:options
* \param receiver_num contains the number of the receiver upon success
*
* This function checks whether \a ra starts with the name of a supported
* paraslash receiver, optinally followed by a colon and any options for that
*
* \param \ra string of the form receiver_name:options
* \param receiver_num contains the number of the receiver upon success
*
* This function checks whether \a ra starts with the name of a supported
* paraslash receiver, optinally followed by a colon and any options for that