developer=true --> DEBUG macro is set, regardless of build type
developer=false --> DEBUG macro is not set, regardless of build type
developer=auto --> DEBUG macro is set only on debug* build types;
this matches old behavior and is the default.
I would've preferred to just go with 4-spaces for indent and no tabs,
but lao is a bit conservative about it. :^)
Still, this is a ton better than mixing different styles all over the
place, especially within the same file.
