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It depends on what kind of change you are making to a header
file. 99% of the time I find that a change to a header is
something innocuous like add a new function, and it still
causes a rebuild of the world. That's particularly annoying
when I'm experimenting with a new object type and adding
things to the header file one at a time -- each time the
header gets touched everything gets rebuilt.

But it's easy enough to only rebuild the core ("make
python") so I'm not sure if I really oppose your simple
solution.