Improve mouse usability for the guest OS.

* When moving the mouse pointer, let the host know where it is.
  This allows the host to ungrab the pointer at the edges of
  the screen and re-grab it when moving back over the VM.

* Hide the mouse pointer in the guest when it's ungrabbed and
  show it again once it becomes grabbed.  This gets rid of the
  orphaned guest pointer that shows up normally when the opentools
  are not installed.

Fixes #1

copypaste.cpp

@@ -118,6 +118,9 @@ static void CopyPasteHelperThread() {
   hab = WinInitialize(0L);
   hmq = WinCreateMsgQueue(hab, 0);
 
+  const auto max_y = WinQuerySysValue(HWND_DESKTOP, SV_CYSCREEN);
+  bool mouse_hidden = false;
+
   for (;;) {
     PointerGetPos(&host_x, &host_y);
     // Handle moving between host and guest.
@@ -126,6 +129,13 @@ static void CopyPasteHelperThread() {
       pointer_home = pointer_home_t::host;
       auto c = GetClipboardFromContents();
       SendClipboardToHost(c);
+
+      // Hide mouse if it's visible.
+      if (!mouse_hidden) {
+	WinShowPointer(HWND_DESKTOP, FALSE);
+	mouse_hidden = true;
+      }
+
     } else if (host_x != XPOS_IN_HOST && pointer_home != pointer_home_t::guest) {
       // Back to the guest
       pointer_home = pointer_home_t::guest;
@@ -142,18 +152,37 @@ static void CopyPasteHelperThread() {
       // Fetch the max screen size for Y since OS/2's coordinates are cartesian
       // (aka bottom right origin) And most others are not (top left origin)
       // Set the guest pointer to match.
-      const auto y =  WinQuerySysValue(HWND_DESKTOP, SV_CYSCREEN) - host_y;
+      const auto y =  max_y - host_y;
       WinSetPointerPos(HWND_DESKTOP, host_x, y);
+
+      // Show mouse if it's hidden.
+      if (mouse_hidden) {
+	WinShowPointer(HWND_DESKTOP, TRUE);
+	mouse_hidden = false;
+      }
 
     }
 
+    if (pointer_home == pointer_home_t::guest) {
+      // Grab the current position, flip it, and send to 
+      POINTL guest_pos{};
+      WinQueryPointerPos(HWND_DESKTOP, &guest_pos);
+      const auto y = max_y - guest_pos.y;
+      PointerSetPos(guest_pos.x, y);
+    }
+
     if (stop_copy_thread.load() == true) {
       log("signal received to end copy thread.");
       break;
     }
 
     // TODO - update guest location based on host position?
-    DosSleep(200);
+    DosSleep(100);
+  }
+
+  if (mouse_hidden) {
+    WinShowPointer(HWND_DESKTOP, TRUE);
+    mouse_hidden = false;
   }
 
   // Cleanup