Fix handling of Python/Guile commands with arguments in gdb-mi.el

Fix handling of Python/Guile commands with arguments in gdb-mi.el

* lisp/progmodes/gdb-mi.el (gdb-python-guile-commands-regexp): New
variable.
(gdb-control-commands-regexp): Use it.
(gdb-send): Don't increment gdb-control-level if the command
matches gdb-python-guile-commands-regexp and has non-empty
arguments.  Reported by David Boles <boles@ieee.org> in
http://lists.gnu.org/archive/html/emacs-devel/2017-06/msg00009.html.