Any change to a Python header file triggers a rebuild of Python core objects. The extension modules are not automatically rebuild in several cases. This is slightly annoying for core development because it forces me to do ``make clean`` too often.

* setup.py adds dependencies on Includes/*.h but not on header files in "internal" and "cpython" subdirectory
* Modules/Setup and makesetup do not add a dependency on PYTHON_HEADERS
* Modules/Setup is also missing dependencies on module-specific headers, e.g. _sre.o should depend on sre.h.