after_git_checkout_note

compilation with -D will not overwrite previously compiled binary, and will lead to Vscode IDE not able to add break point. 

after initial clone:
1. git submodule update --init --recursive
2. Tools/environment_install/install-prereqs-ubuntu.sh -y
3. . ~/.profile
*. rm -rf build/
4. ./waf configure --board sitl
5. ./waf copter --debug
6. cd ArduCopter
7. ../Tool/autotest/sim_vehicle.py --console --map -D
8. after commenting, need recompile to fix src line number of debug binary (a.k.a step 5)

after launch arducopter
fire: "mavproxy.py" "--master" "tcp:127.0.0.1:5760" "--sitl" "127.0.0.1:5501" "--out" "127.0.0.1:14550" "--out" "127.0.0.1:14551" "--map" "--console"