- 'all' in extern/ first builds every subdir, then also 'install's the
header files and the library. This way a top-level Makefile only needs
to call 'all' for extern/ and have it build and install.
- 'clean' still works as it should
ODE does not build on FreeBSD out of the box, so an automated patchfile
is included as well.
The 'clean' target reverses the patches that were done by 'all'.