bug#18282: 24.3.93; Tab completion in gud-gdb at the start of a line overwrites the prompt.

[Stefan Monnier]

>> 1. emacs -Q
>> 2. M-: (gud-gdb "gdb")
>> 3. Type the following at the gdb prompt "hel<TAB><RET>"
>> 
>> What happens is the command "help" is correctly completed, but the
>> prompt "(gdb)" is overwritten.
> Bisected to emacs-24:
>   revno: 114162
>   committer: Stefan Monnier <monnier@iro.umontreal.ca>
>   timestamp: Fri 2013-09-06 18:46:44 -0400
>   message:
>     * lisp/minibuffer.el: Make minibuffer-complete call
>     completion-in-region rather than other way around.
>     [...]

Thanks for bisecting it!  That'll be very helpful,


        Stefan