libgtkhtml-devel (and perhaps all other complex -devel packages) should include dependencies on all _devel_ packages that will be required to build a libgtkhtml-dependant app.
This should include libgal-devel, libgnomeprint-devel etc (check /usr/lib/gtkhtmlConf.sh for the complete list). The list can be easily built w/ a [semi-]automated app that checks appropriate data (using new-style pkgtool or old-style *-config.sh)
Thus we could simplify dependencies list in end-user apps: it would be exactly what is specified in its configure.ac.
Fixed in gtkhtml-1.1.10-alt2