handle setting breakpoints in subfunctions in GUI editor * symtab.h (symbol_table::subfunctions_defined_in_scope): Now public. * debug.h, debug.cc (bp_table::do_add_breakpoint_1): New function. (bp_table::do_add_breakpoint): Handle subfunctions. * ov-usr-fcn.h, ov-usr-fcn.cc (octave_user_code::subfunctions, octave_user_function::subfunctions): New functions. * pt-bp.h (tree_breakpoint::get_line): Return 0 if line wasn't found.