Patch to SLEEP, _KEYHIT, INP(&H60), _SCREENEXISTS for WINDOWS

Change so that modifer keypresses will only register when the window has
focus in Windows.  This corrects the issue with SLEEP, KEYHIT, and
INP(&H60) registering SHIFT, CTRL, and ALT keypresses even when the
program is not in focus or is running as a background app.

Also changed _SCREENEXISTS (and a few other window user commands) so
that they require windows to have actually registered a windows handle
for the function to return -1, and not just for glut to have finished
initializing the screen itself.

internal/c/libqb.cpp

@@ -29469,12 +29469,23 @@ void sub__maptriangle(int32 cull_options,float sx1,float sy1,float sx2,float sy2
     if (key==GLUT_KEY_INSERT){vk=0x5200;}
 
 #ifdef CORE_FREEGLUT
+    #ifdef QB64_WINDOWS
+        if (window_handle==GetActiveWindow()) {
             if (key==112){vk=VK+QBVK_LSHIFT;}
             if (key==113){vk=VK+QBVK_RSHIFT;}
             if (key==114){vk=VK+QBVK_LCTRL;}
             if (key==115){vk=VK+QBVK_RCTRL;}
             if (key==116){vk=VK+QBVK_LALT;}
             if (key==117){vk=VK+QBVK_RALT;}
+        }
+    #else
+        if (key==112){vk=VK+QBVK_LSHIFT;}
+        if (key==113){vk=VK+QBVK_RSHIFT;}
+        if (key==114){vk=VK+QBVK_LCTRL;}
+        if (key==115){vk=VK+QBVK_RCTRL;}
+        if (key==116){vk=VK+QBVK_LALT;}
+        if (key==117){vk=VK+QBVK_RALT;}
+    #endif
 #endif
 
     if (vk!=-1){

internal/c/parts/user_mods/include/steve_mods.h

@@ -32,3 +32,5 @@ double func_sec (double num);
 double func_csc (double num);
 double func_cot (double num);
 int32 func_screenicon ();
+
+extern HWND window_handle;

internal/c/parts/user_mods/src/Steve Stuff/screeninfo.cpp

@@ -1,20 +1,32 @@
 int32 func_screenwidth () {
 	while (!window_exists){Sleep(100);}
+    #ifdef QB64_WINDOWS
+        while (!window_handle){Sleep(100);}
+    #endif
     return glutGet(GLUT_SCREEN_WIDTH);
 }
 
 int32 func_screenheight () {
 	while (!window_exists){Sleep(100);}
+    #ifdef QB64_WINDOWS
+        while (!window_handle){Sleep(100);}
+    #endif
     return glutGet(GLUT_SCREEN_HEIGHT);
 }
 
 void sub_screenicon () {
 	while (!window_exists){Sleep(100);}
+    #ifdef QB64_WINDOWS
+        while (!window_handle){Sleep(100);}
+    #endif	
     glutIconifyWindow();
 	return;
 }
 
 int32 func_windowexists () {
+    #ifdef QB64_WINDOWS
+        if (!window_handle){return 0;}
+    #endif
 	return -window_exists;
 }
 
@@ -24,11 +36,13 @@ int32 func__controlchr () {
 
 int32 func_screenicon () {
     while (!window_exists){Sleep(100);}
+    #ifdef QB64_WINDOWS
+        while (!window_handle){Sleep(100);}
+    #endif
     extern int32 screen_hide;
     if (screen_hide) {error(5); return 0;}
         #ifdef QB64_WINDOWS
              #include <windows.h>
-  extern HWND window_handle;
               return -IsIconic(window_handle);
         #else
           /*     

internal/c/parts/user_mods/src/steve_mods.cpp

@@ -3,5 +3,6 @@
 
 #include "Steve Stuff/convert_angle.cpp"
 #include "Steve Stuff/extramath.cpp"
-#include "Steve Stuff/screeninfo.cpp"
 #include "Steve Stuff/stringcomp.cpp"
+#include "Steve Stuff/screeninfo.cpp"
+