7.4 Python configure hosed

There's a line in config/python.m4 which says:

python_libpath=`${PYTHON} -c "import sys; print sys.path[[1]][[5:]]"`

I think what it's trying to do is cut "/usr/" off the front of the path.
However, if PYTHONPATH is set, or for example, python is installed in
/usr/local/, or if there's a site.py file in the lib directory this
produces the incorrect path (e.g. consider PYTHONPATH=/home/srn/lib -
the line produces /srn/lib).

It's a bit of a pain to have to unset PYTHONPATH. It'd be very nasty if
python isn't installed in /usr/.

Stephen