bug#14282: 24.3; gud-gdb doesn't work

[Jean-Philippe Gravel]

Emacs 24 now uses two separate buffers for GDB and the debugged
program I/Os.  GDB I/Os still go to the *gud-gdb* buffer, but all the
debugged program's I/Os go to the *input/output of ...* buffer.  Once
the program reaches the scanf, you have to switch to the input/output
buffer to provide input.

If you use gdb-many-windows mode, the two buffers will always be
visible to you, therefore reducing the risk of confusion.

There used to be a variable gdb-use-separate-io-buffer that would
allow you to decide where you'd want the program I/O to go.  This
option is gone with the new gdb-mi interface, but I don't know why.