The latest releases of Solaris now ship with the X.org Xserver, so it is
better to use the Xfree Xinerama interfaces if available.  This commit fixes
the configure script so that it first tries to use the Xfree interfaces and
only falls back to the Solaris-specific interfaces if they are not available.
This way, older releases of Solaris which do not use X.org also will work.
(Bug 580079)