automake 1.16.4 and new PYTHON_PREFIX

[Víctor López]

Hello,

After reading the 1.16.4 patch notes regarding PYTHON_PREFIX and the 
discussion that originated the change in https://bugs.gnu.org/35322, I'm 
still not sure if this is expected:

> cat configure.ac
AC_INIT([foo], [1.0])
AM_INIT_AUTOMAKE([foreign])
AM_PATH_PYTHON
AC_CONFIG_FILES([Makefile])
AC_OUTPUT

> cat Makefile.am
python_PYTHON = foo.py

> touch foo.py

> autoreconf -fi

> ./configure --prefix=/tmp/foo && make install
/usr/bin/install: cannot create regular file 
'/usr/lib/python3.9/site-packages/foo.py': Permission denied

Sure, I can use the new flag --with-python_prefix=/tmp/foo, but I feel 
that these changes may have broken a lot of installation scripts and 
outdate the documentation of some packages. Is it intended to be this way?

Thanks