comment FONTFORGE_ARG_WITH_LIBPNG() macro
Fix FONTFORGE_ARG_WITH_LIBJPEG() to hard-stop if "--with" but not there

FONTFORGE_ARG_WITH_LIBJPEG complains of no pkg but doesn't test for it.
Fixed so that ./configure will hard-stop if user requires --with-libjpeg
instead of previous wantings. Added more info in configure.ac and
fixed typos in libpng and libreadline checks.
Fix FONTFORGE_ARG_WITH_LIBTIFF() to hard-stop if "--with" but not there

Ensure libtiff is >= version4.0 by checking for a function removed in 4.0
Check for header and library. Do hardstop if user wants --with but libtiff
doesn't exist, or lower than 4.0, or no developer tiff*.h header files.
Merge pull request #1471 from JoesCat/check_headers_and_libraries_2

hard-stops for with-libjpeg and/or with-libtiff