Plane: break-up scheduling into smaller pieces

ensure mavlink sends don't push us over a scheduling boundary
AP_TECS: Add non airspeed sensor pitch to throttle mode lost during integration
HAL_SITL: Fixing SITL build for OSX.
PX4: A better error message in the log file when the px4io upgrade fails
build: Adding a check for Darwin when adding avrdude.conf's flag for uploading.
ACMotors: bug fix to yaw limit
Copter: yaw limit fix to allow I to reduce

We now allow the I term even if we've hit the yaw limits as long as
updating the I term will reduce it
Copter: remove constraint on rate yaw controller
Coper: compile error fix when FENCE disabled
AP_AHRS: add Roll90Yaw90 to parameter description

Thanks to Rainer Walther for spotting this
Copter: reduce default Loiter Pos P to 0.2 (was 1.0)
WPNav: reduce default WP_ACCEL and LOITER_SPEED
Plane: only call TECS when throttle is not suppressed

this helps prevent integrator buildup on the ground
HAL_AVR: corrected includes to replace #include "$HEADER" with #inlcude "utility/$HEADER"

adding -I for EVERY DIRECTORY isn't desirable

http://gcc.gnu.org/onlinedocs/cpp/Search-Path.html
Copter: added cast to remove compiler warning
HAL_AVR: reorder parameters to remove a warning with -Wreorder
AP_AHRS: make some more functions const
AP_HAL: resolved -Woverloaded-virtual warning

the function:
virtual size_t AP_HAL::Print::write(const uint8_t *buffer, size_t size);

was hidden in all derived classes by their
virtual size_t write(uint8_t) = 0; implementations.

To solve this, a non-virtual write(const uint8_t *, size_t) that calls a
virtual write_implementation was added.

This isn't necessary atm, because the derived classes don't call
write(const uint8_t *, size_t), BUT this decreases the apm2-quad Program
size by 40 bytes :D and removes warnings.
Filter: validity of array index was checked AFTER accessing the element.

(correction decreased Program size by 12 bytes)
extended .gitignore:
.directory (Dolphin's .DS_Store)
/.settings/ (eclipse)