Example Python project demonstrating the python substitution problem.

'prog' is the python package, containing prog/__init__.py and prog/x.py after
       installing.

       prog/x.py is created from x.src using SED

'mk' generates the autotools environment:

     aclocal
     autoconf
     automake --foreign --add-missing --copy

'cfg' does

     ./configure --prefix=/somewhere
     make
     make install prefix=`pwd`/installed

installs at pwd/installed.

Expected output: cat `pwd`/installed/lib/python2.5/site-packages/prog/x.py
returns

def prn():
    print "Libexec=/somewhere/libexec"



Tested with
    autoconf 2.59, automake 1.9.6
    autoconf 2.69, automake 1.11.1
