Don't copy GDAL API C files in clean target.

[sebastic]

da85e95 broke the clean target again, because it changes the sources when it shouldn't. This was fixed earlier via #322.

[sgillies]

It's a little more complicated than this. The source distribution contains an ogrext1.c and an ogrext2.c file now and we use the one suited to the builder's GDAL API version. I'm going to make a new PR that does this without copying files.

Can you remind me how the clean target is used within a Debian build @sebastic?

[sebastic]

The separate targets are called in the various stages of the build:

python setup.py clean
python setup.py config
python setup.py build
python setup.py install --root <DESTDIR>

The clean target is first executed outside the build chroot, and then again inside the chroot as part of the sequence above (which is executed for every Python version).

[sgillies]

Replaced by #362.