Line numbers for shader warnings and errors don't take included files into account

```
The shader loader concatenates everything and then gives back line numbers 
based on the concatenation. However, it could keep track of the line 
numbers for each included file and provide a more helpful error message.
```

Original issue reported on code.google.com by `forrester.cole@gmail.com` on 9 Mar 2009 at 3:37
