If `argc` is `-1`, `block` parameter is sometimes overwritten.

Clear all old flags, even if we change the gc mode during the major gc.

Fix disappearance of command_call in case of statement without parentheses

supress cast warning on C++.

Use new mrb_get_args binary specifier.

mrb_field_write_barrier paints also gray in the major collector.

These objects will be traversed after a minor collect cycle.

Remove multiple definition of RuntimeError.

Error check inprovements in cdump and dump

silence clang warning

src/cdump.h: Use error codes defined in mruby/cdump.h.

Modify `Range#initialize`

Doesn't clear black of all marked objects in the major collector.

fix typos

Since the minor collector doesn't need to mark these objects, the worst-case pause time is reduced.