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)
AP_Compass: fixed rotations for COMPASS_ORIENT

this matches AHRS_ORIENTATION again
AP_Math: make the rotation numbers easier to find
Copter: relax pre-arm checks for mag field

previously it was 50% ~ 150% of expected mag field but now expanded to
35% ~ 165%.
AP_GPS: added explicit cast to omit [-Wconversion] warning
Copter: fixed a compiler warning

* removed useless comparison: if (int8_t t >= 255) ...
* revealed by -Wtype-limits
* saved 6 bytes
AP_Compass: removed comparison out of range compiler warning

uint_ >= 0 (-Wtype-limits)
AP_Param: fixed some compiler warnings

* added comment
* replaced "~0" with the appropriate macro
* resolved -Wconversion
* saved some space by modifying AP_Param::add_vector_suffix (writing
behind buffer could happen, if buffer_size is almost uint16_max but this
can surely be ignored)

further reading:
http://stackoverflow.com/questions/809227/is-it-safe-to-use-1-to-set-all-bits-to-true
AP_Param: fixed a compiler warning with -Wsign-conversion
autotest: external timeout must be greater than internal timeout

or we can get blank output