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/lib/DtXinerama/DtXinerama.c

@@ -0,0 +1,103 @@
+/*
+ * CDE - Common Desktop Environment
+ *
+ * Copyright (c) 1993-2013, The Open Group. All rights reserved.
+ *
+ * These libraries and programs are free software; you can
+ * redistribute them and/or modify them under the terms of the GNU
+ * Lesser General Public License as published by the Free Software
+ * Foundation; either version 2 of the License, or (at your option)
+ * any later version.
+ *
+ * These libraries and programs are distributed in the hope that
+ * they will be useful, but WITHOUT ANY WARRANTY; without even the
+ * implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR
+ * PURPOSE. See the GNU Lesser General Public License for more
+ * details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with these librararies and programs; if not, write
+ * to the Free Software Foundation, Inc., 51 Franklin Street, Fifth
+ * Floor, Boston, MA 02110-1301 USA
+ */
+/*
+ * Jon Trulson, Xi Graphics 4/11/2001
+ *
+ * $XiGId: DtXinerama.c,v 1.1 2001/04/12 03:01:14 jon Exp $
+ *
+ * A Xinerama wrapper for CDE
+ *
+ */
+
+#include <stdio.h>
+#include <unistd.h>
+#include <stdlib.h>
+#include <X11/Xlib.h>
+
+#include "DtXinerama.h"
+
+/* return a DtXineramaInfo_t (or NULL if no Xinerama) available */
+
+DtXineramaInfo_t *_DtXineramaInit(Display *dpy)
+{
+  DtXineramaInfo_t *tmpDtXI = NULL;
+  XineramaScreenInfo *XinerScrnInfo = NULL;
+  int number = 0;
+
+  if (!dpy)
+    return(NULL);
+
+  XinerScrnInfo = XineramaQueryScreens(dpy, &number);
+
+  if (number <= 0 || XinerScrnInfo == NULL) /* then we don't have it */
+    return(NULL);
+
+				/* allocate some space for it */
+  if ((tmpDtXI = (DtXineramaInfo_t *)malloc(sizeof(DtXineramaInfo_t))) == NULL)
+    {				/* malloc failure */
+#ifdef DEBUG
+      fprintf(stderr, "_DtXineramaInit: malloc failed\n");
+#endif
+      
+      free(XinerScrnInfo);
+      return(NULL);
+    }
+
+  tmpDtXI->numscreens = number;
+  tmpDtXI->ScreenInfo = XinerScrnInfo;
+
+  return(tmpDtXI);
+}
+
+
+/* Return w, h, xorg, and yorg for the specified screen.  Return True */
+/* if a valid screen, False otherwise */
+Bool _DtXineramaGetScreen(DtXineramaInfo_t *DtXI, unsigned int screen,
+			  unsigned int *w, unsigned int *h, 
+			  unsigned int *xorg, unsigned int *yorg)
+{
+
+  if (DtXI == NULL)
+    return(False);
+
+  if (DtXI->numscreens == 0)
+    return(False);		/* no screens or no Xinerama */
+
+  if (screen < 0 || screen >= DtXI->numscreens)
+    return(False);		/* invalid screen */
+
+				/* now get the info from the XinerInfo */
+				/* struct and return it */
+
+  if (w != NULL)
+    *w = (DtXI->ScreenInfo[screen]).width;
+  if (h != NULL)
+    *h = (DtXI->ScreenInfo[screen]).height;
+  if (xorg != NULL)
+    *xorg = (DtXI->ScreenInfo[screen]).x_org;
+  if (yorg != NULL)
+    *yorg = (DtXI->ScreenInfo[screen]).y_org;
+
+  return(True);
+}
+