* automake.in (required_targets): Add the pdf and pdf-am targets.
(initialize_per_input): Likewise.
(scan_texinfo_file): Add pdf to @clean_suffixes.
(handle_texinfo_helper): Output the .pdf dependencies, and define
the PDFS variable.
* lib/am/texinfos.am (TEXI2PDF): New variable.
(pdf, pdf-am): New targets.
(.PHONY): Add pdf, pdf-am, and pdf-recursive.
* lib/am/texibuild.am (.%SUFFIX%.pdf): New rule.