PEAR::isError() -- checks for a 
PEAR_Error object
Description
     isError() examines whether a variable is a
     PEAR_Error object and - optional - 
     contains a specific error message or code.       
    
Parameter
     
- mixed
        $data
 
         variable to check
        
- mixed
        $msgcode
 
         additional error message or error code to check
        
 
    Return value
     mixed - returns TRUE, if the variable was a
     PEAR_Error and, if given, contains 
     $msgcode