added support for DGPS update messages and a 2nd GPS
pymavlink: support DF logs for mavparms.py
pymavlink: fixed text parsing of log file headers
pymavlink: added mavgpslag.py

estimate GPS velocity lag from DF logs
pymavlink: mavtomfile.py generates more MATLAB-friendly m files
pymavlink: fixed timestamps for GPS2 messages
apm: added EKF message

used for testing NavEKF system in SITL