Code Merge Request #4: Patch to make PLplot work with Numpy-2.0.0 (open)

Currently, PLplot does not build with Numpy-2.0.0. I made a bug report ober there (numpy/numpy#26854) and we figured, it is PLplot, which is not using the intended include directory but the "numpy" subdirectory.

This patch corrects the used include dir as wenn as the include statements that are generated by swig.

Best, Jan