Copter: throttle deadzone parameter

Allows increasing or decreasing the deadband size in AltHold, Loiter,
PosHold flight modes
Copter: restore CLI set parameter feature

Added back the ability to set params from CLI
Copter: default LAND_REPOSITION to 1
AP_HAL_VRBRAIN: added management for external relay 1 and 2
AP_relay: added default relay pin for VRBRAIN
VRBRAIN: added startup of internal mag's driver for VR Brain Standard 5
AP_HAL: VRBRAIN corrected EEPROM size and added terrain folder on MicroSD
AP_HAL_VRBRAIN: enable 2nd GPS for VRBRAIN 5
Build: VRBRAIN corrected order of MAG startup
Build: VRBRAIN corrected order of MAG startup for 4.5 board
Copter: AC3.2-rc6 release notes
Copter: version to AC3.2-rc6
Copter: update AC3.2-rc6 release notes

Forgot to add GPS driver buffer overflow item
Copter: update AC3.2-rc6 release notes

forgot compass-not-calibrated bug fix
AP_HAL: added missing CONFIG_HAL_BOARD_SUBTYPE #define for HAL_BOARD_VRBRAIN
VRBRAIN: modified target clean
DataFlash: Added four more channels for logging
Copter: enable mount control with channels > 8 for radios with SBUS.
AP_Compass: VRBRAIN. Deal with external mag connected on internal I2C on VRBRAIN 4.5
This enables user to set the external parameter to true even if only one compass is connected