* src/roff/troff/input.cpp (string_iterator::fill): Protect against

* src/roff/troff/input.cpp (string_iterator::fill): Protect against
null pointer.

* tmac/papersize.tmac: Convert `paper' string contents to lowercase.

* configure: Regenerated.

* NEWS: Updated.

Integrate `pdfmark' into normal groff build system;
install macro `pdfmark' packages, build and install `pdfroff',
and PDF format documentation.

* Makefile.comm: Add PDFDOCDIR.

* Makefile.in: (MDEFINES) ALT_AWK_PROGS, ALT_GHOSTSCRIPT_PROGS,
pdfdocdir, make_pdfdoc, make_install_pdfdoc: New variables.
(unstall_dirs): Add pdfdocdir.

* aclocal.m4: (GROFF_APPRESDIR_OPTION): use AC_HELP_STRING instead
of AS_HELP_STRING.
(GROFF_GHOSTSCRIPT_PREFS): New function; support `--with-alt-gs'
option, set ALT_GHOSTSCRIPT_PROGS.
(GROFF_GHOSTSCRIPT_PATH): Support `--with-gs' option, force use of
GROFF_GHOSTSCRIPT_PREFS, set GHOSTSCRIPT.
(GROFF_HTML_PROGRAMS): Force use of GROFF_GHOSTSCRIPT_PATH; tidy up.
(GROFF_AWK_PREFS): New function; support `--with-alt-awk' option,
set ALT_AWK_PROGS.
(GROFF_AWK_PATH): New function; support `--with-awk' option, force
use of GROFF_AWK_PREFS.
(GROFF_PDFDOC_PROGRAMS): New function; force use of GROFF_AWK_PATH
and GROFF_GHOSTSCRIPT_PATH, set make_pdfdoc and make_install_pdfdoc.

* configure.ac: Add AC_PREREQ(2.56), GROFF_PDFDOC_PROGRAMS.
Remove GROFF_GHOSTSCRIPT_PATH, (forced by GROFF_PDFDOC_PROGRAMS, and
also by modified GROFF_HTML_PROGRAMS).