Another new puzzle! This one isn't particularly deep or complex

Another new puzzle! This one isn't particularly deep or complex
(solving it only requires matrix inversion over GF(2), whereas
several of the other puzzles in this collection are NP-complete in
principle), but it's a fun enough thing to play with and is
non-trivial to do in your head - especially on the hardest preset.

[originally from svn r5967]