Code cleanup for GtkHtml

Just a heads up that I filed a rather lengthy code-cleanup patch for
GtkHtml.  It does the following:

- Fixes almost all compiler warnings.

- Migrates the code off most deprecated GTK+ widgets and symbols.

- Prefers gnome-icon-theme icons over it's own redundant PNG files.

The patch seems to be working well for me, but additional testers would
be beneficial.

http://bugzilla.gnome.org/show_bug.cgi?id=394182

Thanks,
Matthew Barnes