Share GraphicsBitmaps between the windowing server and the client process.

This is pretty cool. :^)

GraphicsBitmaps are now mapped into both the server and the client address
space (usually at different addresses but that doesn't matter.)

Added a GUI syscall for getting a window's backing store, and another one
for invalidating a window so that the server redraws it.

LibC/stdlib.cpp

@@ -215,4 +215,18 @@ long atol(const char* str)
     return atoi(str);
 }
 
+
+static unsigned long s_next_rand = 1;
+
+int rand()
+{
+    s_next_rand = s_next_rand * 1103515245 + 12345;
+    return((unsigned)(s_next_rand/((RAND_MAX + 1) * 2)) % (RAND_MAX + 1));
+}
+
+void srand(unsigned seed)
+{
+    s_next_rand = seed;
+}
+
 }