This is necessary to run Python programs from pybin_scripts during
an out-of-srcdir build. We need to be able to run programs from
pybin_scripts during the build *before* we install them in order to
do unit tests and in order to generate manpages using help2man.
The reason is that whenever you run a Python script, "the directory
containing that file is added to the start of sys.path, and the file
is executed as the __main__ module" (see
https://docs.python.org/2/using/cmdline.html). It turns out that if
the script is a symbolic link, then the symbolic link is *followed*
before modifying sys.path. As a result, during an out-of-srcdir
build, the first element of the Python path is the source directory
that contains the script, which does *not* contain the SWIG
Python C extension module.
An alternative workaround would be to make sure that the sources of
the pybin_scripts files are not in the same source directory as the
modules.
Original: 42c80fcd911ad5206f2a085d217bd5c79acee826