[patch][doc] Fix PR python/15613 (make gdb.GdbError formatting consistent with other exceptions

[Eli Zaretskii]

> Date: Wed, 18 Sep 2013 21:02:42 +0100
> From: Phil Muldoon <pmuldoon@redhat.com>
> 
> This patch addresses PR 15613.  This makes the formatting of
> gdb.GdbError more consistent with other exception types documented.
> 
> OK?

OK for the documentation part.

Thanks.