install.sh doesn't work correctly if -p is given before -P

[AlisterH]

There is a bug in install.sh If I do this:

./install.sh -p /usr -P /usr/bin/python2 

then I get this, and the files are not installed properly:

  File "<string>", line 1
    import distutils.sysconfig; print distutils.sysconfig.get_python_lib()
                                              ^
SyntaxError: invalid syntax
Installing gtk version of cropgui
Installed cropgui gtk

If I do this it works:

./install.sh -P /usr/bin/python2  -p /usr

[jepler]

[I'd rather burn down install.sh and make this set up & run via modern Python packaging methods e.g., pyproject.toml & pip install]