uselib is no longer implicit (inherited by .use). This is still incomplete,
some uselibs for non-linux variants may be missing.
bld.is_defined("HAVE_XXX") also no longer works and will have to be
changed (I think to bld.env["HAVE_XXX"]) in countless places.
Those objects do not have a versioned API by themselves.
This fixes issues with duplicate deployment (OSX, Linux bundles: cp) and
ardour listing control-surfaces multiple times (file index plugin dir).
