Minor update to ImageMagick 6.5.7-10

ImageMagick 6.5.7-8 is no longer available.
Patch texinfo to be compatible with dash.

dash (and possibly other shells) refuses to override builtins.
Don't build info docs for gcc and guile.

They use makeinfo from the system and tend to lead to fail builds
on syntax errors in the doc files. We don't need the docs anyway.
Don't run the dblatex regression tests.

They use dblatex from the system and tend to fail.
Replace literal python, use the $(PYTHON) macro instead.
Avoid TypeError: issubclass() arg 1 must be a class.
Print help message when running bin/gib without args.
Remove literal bin/gub, use $(GUB) macro instead.
Remove unnecessary lambda.