refs #18 - add zope.app.component to install_requires for <=4.3 compatiblity
refs #18 - buildout for 4.3 latest based on buildout.plonetest
refs #18 - add adapter that returns p.a.imaging ImageTraverser. wire up adapter in zcml
refs #18 - remove IImagingSchema from subscriber adapter decorator. that wasn't reall the right place for it