shells/rc 1.7.4_5 DragonFly

This is a reimplementation for Unix, by Byron Rakitzis, of the Plan 9 shell. The original rc was designed and implemented by Tom Duff at Bell Labs. It has a small feature set similar to a traditional Bourne shell, but with a much cleaner and simpler syntax. Among other things, this makes rc much better than Bourne-compatible shells at handling filenames which contain spaces. Thus, writing rc scripts is less error-prone than writing sh scripts.