[texhax] Passing Underscore

[Karl Berry]

    Thanh et al

As far as I know, the new \input "..." feature was written by Olaf Weber
in core Web2c, not as part of pdftex.

    chose to use double quotes as delimiters 

Clearly it is not a general solution.  However, it now means there is an
easy way to use filenames with spaces, which was its intent.  That's all.

Adding new primitives is beyond what Web2c should do (IMHO); a general
solution in pdfetex would be very welcome, to me at least.

    what is it that you /want/ to happen ?

I assume just "Makefile", without the ".tex" extension.  Again, this is
something that would need to be addressed with a new primitive (or
parameter), seems to me.

k