[WIP] update mac configure script and add messaging about common port forwarding issue

update mac configure script and add messaging about port forwarding until we maybe use a better solution like how libtorrent does this, or RPC & UDP like this https://github.com/bmuller/rpcudp to avoid most port forwarding issues.
>then this won't do anything.
not necessarily true, although I know what you mean @tikhon 

I think it's better to do something along these lines

```
# got python?
if command_exists python ; then
    # make sure it's not too old
    old_python=`python -c 'import sys; print("%i" % (sys.hexversion<0x20708f0))'`
    if $old_python ; then
        brew install python
    fi
else
    # no python? easy peasy
    brew install python
fi
```