* breakpoint.c (add_catch_command): Use completer_ftype.
* breakpoint.h: Include command.h.
(add_catch_command): Use completer_ftype.
* cli/cli-decode.c (set_cmd_completer): Use completer_ftype.
* cli/cli-decode.h (struct cmd_list_element) <completer>:
Use completer_ftype.
* command.h (completer_ftype): New typedef.
(set_cmd_completer): Use it.
* python/py-cmd.c (struct cmdpy_completer) <completer>: Use
completer_ftype.