Plane: make GPS UART blocking again
Rover: make GPS UART blocking again

until we have support for non-blocking config packets in uBlox
Copter: reduce twitch when entering CIRCLE mode

Set loiter target and prev iterations velocity when circle mode is
started
Start circling from projected stopping point
WPNav: add acceleration parameter

WP_ACCEL added to allow user control of acceleration during missions.
Loiter acceleration made to be half of loiter max speed
Copter: update AC3.0-rc6 version and release notes
Copter: reduce default AltHold P to 1.0 (was 2.0)

This helps reduce jumpiness due to althold feed forward
Copter: add @Increment to PID parameters descriptions
Copter: update firmware version to 3.0.0
PX4: Remove -Os because I've changed the px4 tree to have that as the
default
AP_Baro: TEMP parameter comment fix
autotest: fixed pymavlink tools paths
autotest: fixed handling pf pymavlink paths
Copter: update FS_THR_VALUE parameter description

One user was setting FS_THR_VALUE too low, below 900 which means
ArduCopter would not trigger when the ppmencoder pulled ch3 low after
updates from the ppmencoder stopped
Rover: update FS_THR_VALUE parameter description
Plane: update THR_FS_VALUE parameter description
autotest: fixed import of mavwp
autotest: added $HOME/APM to PYTHONPATH