[R6RS] script syntax

[dyb at cs.indiana.edu]

> I've removed the "#!/usr/bin/env" comment rule from the grammar in 
> lex.tex, and change scripts.tex to mention that text after "#!" on the 
> first line of a script must be ignored.
>
> I didn't say anything about the third character needing to be space or 
> "/".  If anyone thinks that's necessary, yell.

Before noticing your email, I already changed it to require only that
a first line starting with #!<space> or #!/ be ignored, and provided
a rationale in the commit comment.  Basically, a reasonable local
customization of the script on a Windows platform might be to eliminate
the first line altogether, and a following line of #!r6rs or some
other #!symbol would then be incorrectly ignored.

Kent