Support for symbols in msg-type of make-message

[gaya-]

Currently, the msg-type argument of make-message has to be a string of format "package/message_type":

CL-USER> (roslisp:make-message "geometry_msgs/Twist"
                               (:x :linear) 1
                               (:z :angular) 2)
[GEOMETRY_MSGS-MSG:TWIST
   LINEAR:
     (GEOMETRY_MSGS-MSG:VECTOR3 (:X . 1) (:Y . 0.0) (:Z . 0.0))
   ANGULAR:
     (GEOMETRY_MSGS-MSG:VECTOR3 (:X . 0.0) (:Y . 0.0) (:Z . 2))]

I suggest also supporting class name as message types, similar to how it is done with services:

CL-USER> (roslisp:call-service "/spawn" 'turtlesim-srv:spawn
                               :x 5 :y 5 :theta 1.0)
CL-USER> (roslisp:make-request "moveit_msgs/getpositionfk")
CL-USER> (roslisp:make-request 'moveit_msgs-srv:getpositionfk)

1. Using strings here instead of actual message classnames is not very convenient, because if one forgets to add a dependency on the message package the failure will only come up at runtime.
2. Another advantage of using symbols is that it has autocompletion
3. One can also jump straight to the message definition if it's a valid classname

This PR will then allow:

CL-USER> (roslisp:make-message 'geometry_msgs-msg:twist
                               (:x :linear) 1
                               (:z :angular) 2)