Add support for xdebug memory usage tracing (xdebug.trace_format = 1)

```
It would be great if webgrind could handle xdebug's new trace format which 
includes memory usage.

Se more on:
http://derickrethans.nl/xdebug-and-tracing-memory-usage.html
```

Original issue reported on code.google.com by `carlshol...@gmail.com` on 29 Jun 2010 at 8:34
