[texhax] Detection of start of source line

[Philip Taylor]

Philip Taylor wrote:
> But now that the cat has got off and I am wearing the right glasses, I can confirm that my suggestion does not work as-is; even when \futurelet has changed \nexttoken into the character '*', the \ifx fails, for reasons that temporarily escape me ...
The main reason being that I cannot spell consistently :  \nexttoken v. \nextoken.  But with that corrected, even more horrible errors occur, so I must leave this in abeyance for a while ...