Plane: fixed spelling
autotest: fixed autotest executable path
autotest: bumped version number of QUpgrade

rebased (pch) - closes pull request 184
Added Vagrantfile to define a standardized Ubuntu 12.04 32-bit
development environment.

Added a script, install-prereqs-ubuntu.sh, that installs all packages
and software required for development on AVR and PX4 platforms.

pch: rebased pullreq 183
Updated README:

 * Added instructions on installing prerequisites in (Ubuntu) Linux.
 * Added instructions on how to use vagrant for development.
 * Minor copy-editing.

pch: rebased pullreq 183
autotest: APM xml docs should be named xml.pdef.xml

(not arduplane.pdef.xml)

pch: rebased pull request #188
documentation: explain what a 'sketch' is.
documentation: explain where the build output goes.

pch: rebased pullreq #189
InertialSensor: added OilPan INS example
autotest: fixed sleep_overhead calculation in sim_multicopter.py
AP_Camera: enable relay off in all builds
cleanup: use const for struct Location pointers and references

this allows the compiler to generate more efficient code
INS: updated MPU6K_FILTER parameter description
Copter: remove old commented out code from setup.pde
Copter: bug fix for loiter target
Plane: avoid doing radio trim if less than 20% of travel available

this prevents problems with awful trim on bootup due to RC TX being
off
AP_Navigation: added a navigation controller class

the new L1 controller will be a instance of this class. Other
navigation controllers can be added as additional instances

Pair-Programmed-With: Paul Riseborough <p_riseborough@live.com.au>
AP_Math: added Vector2f.angle()

useful for calculating the vector in polar coordinates
AP_Math: fixed grammar error
AP_Math: added RadiansToCentiDegrees and RADIUS_OF_EARTH