Fix issue chjj/tty.js#59

^[[>##m and ^[[>##n are legal escape sequences, but were being parsed as if they were ^[[##m or ^[[##n. Added a test for prefix character ('>' is the only legal one)  

See http://invisible-island.net/xterm/ctlseqs/ctlseqs.html, code for CSI > P s ; P s m

If the prefix char is present, ignores the control sequence, since that code isn't implemented.