Use a much shorter timeout for normal communication, and stretch it only when we are waiting for erase.

ORB topic advertisements are now global handles that can be used in any context.  It is still possible to open a topic node as a publisher, but it's not the default.  As a consequence, the type of the handle returned from orb_advertise has changed; all other API remains the same.

Fix output scaling for the hmc5883 driver.  Add data checking, and fix an issue where the ORB topic could not be published due to being advertised in the wrong context.

Fix an issue where the baro ORB topic was advertised from the wrong context and thus could not be published to.

This is part of \#7

Updated ROMFS scrips, created new ardrone_interface to jointly use multirotor_att_control on all multirotors, including AR.Drone frames

Added deamon example, reworked / merged multirotor attitude control. Ready for AR.Drone interface changes and integration tests

Cleaned up position control (WIP), moved PID structs (should become classes) to systemlib, added deamon app example

Stop using systemlib in the PX4IO firmware; it has expectations that can't reasonably be met.

'make clean' at the top level should 'distclean' in NuttX, as it's not obvious otherwise how to get NuttX to clean out its dependencies and app configuration.

Add <err.h> modeled on the BSD functions of the same name; this will let us clean up a lot of output from various shell tools.

Fixed PI wrapping code, debugging more sensor code, possible misalignment of mag and acc frames in filter