make pygmalion theme use two lines when needed

if the length of the prompt (excluding color escapes) exceeds 40 characters, emit the arrow prompt on its own line

This helps a lot on smaller terminals

Illustration: 

![illustraion](http://i.imgur.com/QHQWi.png)

The top prompt is the default look, the second one has a path that exceeds 40 characters and thus is shown on two lines.

Is it ok to update an existing theme like this or do you prefer if I create a pilif theme that has this extension?