bug#21521: 24.5; pdb default suggested command

[Eli Zaretskii]

> From: Stefano Pacifico <github@pacifico.cc>
> Date: Tue, 22 Sep 2015 15:20:42 -0400
> Cc: 21521@debbugs.gnu.org
> 
> Because it does not seem that standard distributions of Python install a 
> `pdb` executable script in standard PATH locations. This wiki, for example, 
> https://wiki.python.org/moin/EmacsEditor suggests creating the link manually. 
> 
> On the other hand, all distributions of Python come with the `pdb.py` module 
> available by default, so `python -m pdb` should always work. 

Is this a Python-only problem or are there other debuggers supported
by GUD with similar issues?