bug#8289: distcheck and make dvi

[Ralf Wildenhues]

* Karl Berry wrote on Sun, Mar 20, 2011 at 10:28:59PM CET:
>     not bother checking dvi output and rather test PDF output seems
>     like another good alternative.
> 
> I can't agree with that.  That's trading DVI-generation problems for
> PDF-generation problems.  Believe me, there will be just as many if not
> more.  Any manual which has *only* eps files, for starters.

Right, I'm on the same page as you here: such a trade should be at the
developer's discretion.

> All together, for a general fix, my suggestion is to simply replace the
> hardwired "dvi" string with a new variable name, like
> $(AM_DISTCHECK_DOC) or some such (no idea if that's a reasonable name,
> but you get the idea), which defaults to dvi and which users can
> override either with "pdf" or with some no-op target.  Which in turn
> would need to be created/documented if one doesn't exist already.

Something like that sounds sensible.  Incidentally, Stefano already has
a pending patch for some distcheck generalizations using variables; the
change for this PR could look to use similar style.

Cheers,
Ralf