Add basic Xinerama support via new lib/DtXinerama

This adds a basic library and support to dtsession and dtlogin to
support Xinerama/Twinview, where multimple monitors are used to make
up an X11 screen.

The main goal here is to draw dialogs and such centered on a monitor,
rather than spread out over multiple monitors.

Might need to add sorting - as on my test system, what I would
consider monitor 0, appears to actually be monitor 1.  So a sort might
need to be added to sort the screens according to increasing x and y
offsets so it make sense to a user.

Also, this library is built statically and not documented.  Maybe it
could be 'filled' out and refactored/redesigned in the futre if need
be and suppoerted.

It is enabled via a define, CDE_USEXINERAMA in site.def.  It's a very
simple lib, so I do not expect any issues with the BSD's - it should
build and work fine, assuming your X server has the XINERAMA
extension, which I think pretty much all of them do at this point.

cde/programs/dtsession/SmMain.c

@@ -70,6 +70,9 @@
 #include <Dt/EnvControlP.h>
 #include <Dt/DtP.h>
 #include <Dt/Lock.h>
+#ifdef USE_XINERAMA
+#include <DtXinerama.h>		/* JET - Xinerama support */
+#endif
 #include "Sm.h"
 #include "SmError.h"
 #include "SmGlobals.h"
@@ -387,6 +390,25 @@ main (int argc, char **argv)
         SM_EXIT(-1);
     }
 
+    /* JET - initialize for Xinerama, if present 4/12/2001 */
+#ifdef USE_XINERAMA
+    smGD.DtXineramaInfo = _DtXineramaInit(smGD.display);
+
+# ifdef DEBUG
+    if (smGD.DtXineramaInfo == NULL)
+      {                         /* No xinerama, how... sad. */
+        fprintf(stderr, "### JET SmMain: Xinerama NOT available.\n");
+      }
+    else
+      {
+        fprintf(stderr, "### JET SmMain: Xinerama available, scrns = %d\n",
+                dpyinfo.DtXineramaInfo->numscreens);
+      }
+# endif
+
+#endif
+
+
    /*
     * Restore preferences
     */