add (+document) the function for displaing the actual flag values

```
for debugging output it would be helpful to have the method iterating all the 
flags and showing the value set for the current call provided with shflags.

It could make error analysis easier and would take the burden from the script 
developer to do so manually if needed.
```

Original issue reported on code.google.com by `butko...@gmail.com` on 8 Jul 2013 at 9:35
