FastSerial: make interface 8 bit and add write_buffer_nonblock() call

this saves a fair bit of CPU for ArduCopter
GCS_MAVLink: fixed const in buffer based send call
AP_Param: added copy_name_token() interface
Copter: ensure we process deferred mavlink messages
Copter: use AP_Param::copy_name_token()
Copter: minor mavlink cleanup
MPU6000: use expected sample time, not actual sample time

this avoids problems in the scheduler turning up as errors in the DCM
calculation. The MPU6k produces samples with more reliable timing than
our scheduler does!
GCS_MAVLink: use AVR assembler CRC function if available