Skip m4 on Tiger and later

Make good on the comment in bootstrap.modules that says you can skip
building m4 on new enough OSXs.
Fix outdated comments

We now don't skip bison and flex at all, so remove the comments saying we
do.
Update osx-bootstrap modules to newer versions

libpng, libjpeg, libxml2, and libxslt can all be simply updated to newer
versions.
Update libtiff

libtiff's newer version doesn't need the --without-apple-opengl-framework
configure switch, so delete that as well.
Update hicolor-icon-theme

Version 0.13 does support non-srcdir builds, so remove that flag.
Update gettext-runtime

This version doesn't need the patch for bug 33999 anymore, so we can
remove that patch file.
Add itstool

This is a quite common build dependency in Gnome lately.
Update gtk-doc, replace gnome-doc-utils with yelp

The latest gtk-doc needs itstool and libxml2, so it needs to go into
gtk-osx-bootstrap.modules.

The gnome-doc-utils module has been superseded by yelp-tools and
yelp-xsl.
Update comments on 10.10 versions of tools