Minor bug-fixing update.

• Music muting now fully works.
• Added a barrier before the last ceiling portion of level 1-7.
• Rope no longer extends past the bottom of the screen if used above a pit.
• Checkpoint collision box doubled so it's easier to hit.
• Can no longer get past scrolling barriers by going over the top of the screen.
• More hardware single-frame sprite problem fixes. (OAM decay)