use the data copying custom compiler approach here, too.
this leaves more work to qmake, which is good.
on the upside, pluginspecs will be installed when they change without
having force a re-link of the plugin itself.
on the downside, installation of a pluginspec will force a re-link of
the plugin. oh, well - you can't have it all (with qmake) ...
now bin and share are not pegged to linking the executable any more,
but are proper subdirs targets of their own.
unforturnately, qmake is a bit tenacious, so we hack around a bit. :)
more or less in passing by, i removed some superfluous trailing slashes
and added path normalization as well.
