DataFlash: fixed logging on PX4v1

large writes break IO, a NuttX bug
Git: ignore LASTLOG.TXT
AC_WPNav: set loiter accel to 1/2 of speed

Bug fix from Leonard.
Also fixed some formatting.
Copter: add EKF params to full param list
Rover: add EKF params to full param list
Plane: reserve NavEKF slot in param list even when not used

Although this wasn't a problem immediatley, if someone had added a
parameter after k_param_NavEKF it's position in eeprom could have moved
as AP_AHRS_NAVEKF_AVAILABLE was enabled/disabled
InertialSensor_PX4: resolve compiler warning
Git: ignore Build.APMrover2 directory
AP_Math: make is_nan const for quaternion and add .zero() for vector2
AP_NavEKF: allow states to be accessed using names as well as a Vector22
AP_HAL: added support for commandline arguments

useful for log replay, specifying log file
AP_InertialSensor: allow HIL sensors to support multiple instances

this allows log replay to test both sets of sensors on a Pixhawk log
AP_NavEKF: allow log filename to be specified in replay
AP_NavEKF: support dual sensors in log replay, and fix flight altitude
Rover: fix for HIL API change
Copter: fix for HIL API change
Plane: fix for HIL API change
Plane: fixed logging of relative altitude
HAL_SITL: fixed build with new HIL INS API
AP_InertialSensor: enable get_accel_count() and get_gyro_count() APIs for HIL