Fix double prompt of 'interpreter-exec mi'.
* mi/mi-interp.c (mi_execute_command_input_handler): New prototype.
(mi_interpreter_resume): use it.
(mi_execute_command_input_handler): New function.
* mi/mi-main.c (mi_execute_command): Move prompt printing to
mi_execute_command_input_handler.
gdb/testsuite/
* gdb.mi/mi2-prompt.exp: New file.
