/usr/local/lib.
This removes the need to add to shlib_dirs.
HOWEVER, ports that depend on these should explicitly use
-L/usr/local/lib/qt or -L/usr/local/lib/qt2 to be sure to grab the right
library, even if the other library is installed as well.
Add qimgio support (other graphics formats).
This adds a build time dependency, but no runtime dependency,
as users have to explicitly link against libqimgio, as of qt 1.xx
