make sure filename is relative
make sure filename is relative

the __main__ makes sure that the input filename is
specified as a relative path, but other programs
that call compileFunction directly bypass this.
We already check whether the filename can be
converted to a relative path (when we check that
the filename is actually a filename) so all we
need to do is keep the result and use it (if it
is a filename)

BBN-Q/pyqgl2,BBN-Q/pyqgl2