a small I value is good on most planes, so I think this is a better
default than 0. Thanks to Chris for asking about this.

this gives a more accurate picture of what is actually happening with
the servos

This is better since each project has very different options.

this makes it possible to fetch parameters with very low air data
rates

streams can now be requested at any multiple of 20ms. So if you ask
for a stream at 7Hz then you will get it at close to 7Hz.

the GPS_STATUS message is a massive waste of bandwidth, but it is the
only message that tells us the number of visible satellites. So only
send it if that information changes.

This makes MAVLink work better at low baud rates

the 128 byte serial transmit buffer was causing significant problems
with queueing of mavlink messages. With 256 bytes we can fit a lot
more messages out in each pass of the code, which makes telemetry more
efficient

As we discussed on the dev call, we now have enough free ram for this
to be worthwhile

when MANUAL_LEVEL is set to 1, we don't do accelerometer levelling at
startup, and instead used the values saved in the EEPROM. This makes
it easier to do levelling on the bench, or once for a series of
flights for the day

if someone tries to set a AP_Int16 to a value of 300000, they now get
32767 instead of -27678

these options are now settable via MAVLink

unfortunately this library was causing avrdude to fail to load the hex
to my APM2. Until we work out why, it's disabled.

AP_Declination: Added call to compass.set_initial_location if the compass is enabled when the 3D fix is obtained.

Signed-off-by: Andrew Tridgell <tridge@samba.org>

AP_Declination: Added new config value to allow the user to have the declination overwritten on every 3D fix.

Signed-off-by: Andrew Tridgell <tridge@samba.org>