AP_Mission: Give CONINTUE_AND_CHANGE_ALT a parameter: climb/descend

Param 1 denotes which direction the user expects the plane to
travel when changing altitude:

0 = no expectation, command completes when within 5 m of altitude.
1 = climb expected, command completes at or above altitude.
2 = descent expected, command completes at or below altitude.

libraries/AP_Mission/AP_Mission.cpp

@@ -531,6 +531,10 @@ bool AP_Mission::mavlink_to_mission_cmd(const mavlink_mission_item_t& packet, AP
 
     case MAV_CMD_NAV_CONTINUE_AND_CHANGE_ALT:           // MAV ID: 30
         copy_location = true;                           // only using alt
+        cmd.p1 = packet.param1;                         // Climb/Descend
+                        // 0 = Neutral, cmd complete at +/- 5 of indicated alt.
+                        // 1 = Climb, cmd complete at or above indicated alt.
+                        // 2 = Descend, cmd complete at or below indicated alt.
         break;
 
     case MAV_CMD_NAV_LOITER_TO_ALT:                     // MAV ID: 31
@@ -849,7 +853,11 @@ bool AP_Mission::mission_cmd_to_mavlink(const AP_Mission::Mission_Command& cmd,
         break;
 
     case MAV_CMD_NAV_CONTINUE_AND_CHANGE_ALT:           // MAV ID: 30
-        copy_location = true;                           //only using alt.
+        copy_location = true;                           //only using alt
+        packet.param1 = cmd.p1;                         // Climb/Descend
+                        // 0 = Neutral, cmd complete at +/- 5 of indicated alt.
+                        // 1 = Climb, cmd complete at or above indicated alt.
+                        // 2 = Descend, cmd complete at or below indicated alt.
         break;
 
     case MAV_CMD_NAV_LOITER_TO_ALT:                     // MAV ID: 31