made in the early days of openlayers) but the cache means that relative mouse
positions are off if your first mouse event over the map is *after* the page is
scrolled. This closes#333 , and fixes a long standing not-well understood bug.
git-svn-id: http://svn.openlayers.org/trunk/openlayers@1692 dc9f47b5-9b13-0410-9fdd-eb0c1a62fdaf