isEquivalentURL() not complete for IE

FF:

a.href = barf/barf/fly.html
a.pathname = /~euzuro/foo/bar/barf/barf/fly.html
a.host = www.openlayers.org

a.href = http://www.openlayers.org/~euzuro/foo/bar/barf/barf/fly.html
a.pathname = /~euzuro/foo/bar/barf/barf/fly.html
a.host = www.openlayers.org

windowpath: /~euzuro/foo/bar/test.html

IE:

a.href = barf/barf/fly.html
a.pathname = 
a.host = 

a.href = http://www.openlayers.org/~euzuro/foo/bar/barf/barf/fly.html
a.pathname = ~euzuro/foo/bar/barf/barf/fly.html
a.host = www.openlayers.org:80

windowpath: /~euzuro/foo/bar/test.html

the above comment, IE is IE6

here is IE7:

 a.href = barf/barf/fly.html
 a.pathname = barf/barf/fly.html
 
 b.href = http://www.openlayers.org/~euzuro/foo/bar/barf/barf/fly.html
 b.pathname = ~euzuro/foo/bar/barf/barf/fly.html

It might be more productive to figure out why checkImgURL is needed at all (instead of duplicating the browser's path parser). Maybe that is well understood by others, but it seems a bit voodoo to me (and potentially a memory management issue).

this might be a fix. seems to pass tests tests on ie6, ff, moz, and opera

Applied in r2162. Marking for pullup to 2.3.