Remove fixed-size literal buffer from scan.l, and repair

Remove fixed-size literal buffer from scan.l, and repair
boundary-condition bug in myinput() which caused flex scanner to fail
on tokens larger than a bufferload.  Turns out flex doesn't want null-
terminated input ... and if it gives you a 1-character buffer, you'd
better supply a character, not a null, lest you be thought to be
reporting end of input.