Use exceptions rather than asserts for for "normal" errors

Although these are rare, they are still not indicative of bugs so
an exception (which ends up in the log and might also be shown to
the user) is more appropriate than an assert. Asserts should only
be used to catch blatant API misuse and similar.

vncviewer/OSXPixelBuffer.cxx

 #include <config.h>
 #endif
 
-#include <assert.h>
-
 #include <ApplicationServices/ApplicationServices.h>
 
 #include <FL/Fl_Window.H>
     throw rfb::Exception(_("Not enough memory for framebuffer"));
 
   lut = CGColorSpaceCreateDeviceRGB();
-  assert(lut);
+  if (!lut)
+    throw rfb::Exception(_("Could not create framebuffer device"));
 
   bitmap = CGBitmapContextCreate(data, width, height, 8, width*4, lut,
                                  kCGImageAlphaNoneSkipFirst | kCGBitmapByteOrder32Little);
-  assert(bitmap);
-
   CGColorSpaceRelease(lut);
+  if (!bitmap)
+    throw rfb::Exception(_("Could not create framebuffer bitmap"));
 }
 
 

vncviewer/Viewport.cxx

 
 #include <rfb/CMsgWriter.h>
 #include <rfb/LogWriter.h>
+#include <rfb/Exception.h>
 
 // FLTK can pull in the X11 headers on some systems
 #ifndef XK_VoidSymbol
     fb = new X11PixelBuffer(w, h);
 #endif
   } catch (rdr::Exception& e) {
+    vlog.error(_("Unable to create platform specific framebuffer: %s"), e.str());
+    vlog.error(_("Using platform independent framebuffer"));
     fb = new FLTKPixelBuffer(w, h);
   }
 

vncviewer/X11PixelBuffer.cxx

 #include <config.h>
 #endif
 
-#include <assert.h>
 #include <stdlib.h>
 
 #include <FL/x.H>
   if (!setupShm()) {
     xim = XCreateImage(fl_display, fl_visual->visual, fl_visual->depth,
                        ZPixmap, 0, 0, width, height, BitmapPad(fl_display), 0);
-    assert(xim);
+    if (!xim)
+      throw rfb::Exception(_("Could not create framebuffer image"));
 
     xim->data = (char*)malloc(xim->bytes_per_line * xim->height);
-    assert(xim->data);
+    if (!xim->data)
+      throw rfb::Exception(_("Not enough memory for framebuffer"));
   }
 
   data = (rdr::U8*)xim->data;