bug#7995: Guile support in Automake

Automake should support Guile. (From Ludovic Courtès and Andy Wingo). I actually have patches for some tests, documentation and half an implementation from last year; opening this PR now to track progress and not forget again. Thanks, Ralf

bug#7994: make distcheck fails when latex is not installed

In a package with a texinfo file, distcheck fails when LaTeX is not installed. Instead, it should exit 63(?). The fact that distcheck runs 'make dvi' is not documented. (From Jose; please correct me if I cited this wrongly now.) Thanks, Ralf