XML: added MAV_CMD_NAV_SPLINE_WAYPOINT

This is used to create a spline path waypoint
pymavlink: raise version
pymavlink: draw spline waypoints on map
common.xml: added SERIAL_CONTROL message

this message allows for control of a serial device on a remote
node. This can be used to (for example) update the firmware on a 3DR
air radio by connecting to a Pixhawk over USB.
pymavlink: added MavlinkSerialPort class

this class gives remote serial control of a device via SERIAL_CONTROL
messages
pymavlink: raise version
Added quaternion based gimbal control message
Added two new frames to avoid floating point resolution becoming a critical limit
APM: added MAV_CMD_DO_PARACHUTE

used by new AP_Parachute library
Script to connect u-Center directly to PX4/Pixhawk GPS via Mavlink serial control

Also fixes a couple of small bugs in MavlinkSerialPort.
Merge pull request #176 from matthewlloyd/mavgps

Script to connect u-Center directly to PX4/Pixhawk GPS via Mavlink serial control
Generalize a number of MAV_CMD entries to common message set after discussion with APM developers - no IDs or funcationality changes with already used messages. MAV_CMD_DO_MOUNT_CONTROL updated after discussion, this message is not in use (yet)
pymavlink: added SCAN mode for tracker
pymavlink: raise version
mavtomfile: Make sure m filename is compatible with MATLAB / octave.
mavparm: added check option to load()
pymavlink: raise version
pymavlink: added AUTOTUNE mode for planes
pymavlink: raise version
pymavlink: print skipped message header in DFReader