Use Rel macros for window handle manipulation

Munge between internal and external window handles using the same macro the Wimp does for clarity.

s/CopyFilter

@@ -37,7 +37,7 @@ copy_filter_handler
 
         Push    "r0-r2,r10,r11,LR"
 
-	ADD	r0,r10,#1
+        Rel     r0,r10
 
         LDR     r1,copy_filters
 copy_filter_exit

s/FilterMgr

@@ -83,6 +83,11 @@ debugregister   SETL {FALSE}            ; Register/de-register
 
 wsptr           RN      R12
 
+        MACRO
+$lab    Rel     $to,$from,$cc           ; Turn Abs window handles to Rel
+$lab    ADD$cc  $to,$from,#1
+        MEND
+
 ; ----------------------------------------------------------------------------------------------------------------------
 ;      Filter block structure
                 ^       0

s/PoIcFilter

@@ -41,7 +41,7 @@ post_icon_filter_handler
         MOV     R2,R2,ASL #16
         MOV     R2,R2,LSR #16
 
-        ADD     r0,r10,#1	         ; find the window being redrawn
+        Rel     r0,r10                   ; find the window being redrawn
 
         LDR     r1,post_icon_filters
 post_icon_filter_exit

s/PoRtFilter

@@ -40,7 +40,7 @@ post_rect_filter_handler
         MOV     R2,R2,ASL #16
         MOV     R2,R2,LSR #16
 
-        ADD     r0,r10,#1	         ; find the window being redrawn
+        Rel     r0,r10                   ; find the window being redrawn
 
         LDR     r1,post_rect_filters
 post_rect_filter_exit

s/RectFilter

@@ -49,8 +49,8 @@ rect_filter_handler
         LDR     r0, get_handle_from_r10 ; find the window being redrawn
         TEQ     r0, #0
         LDREQ   r0, [sp,#16+12+0]	; BTW - you didn't see that...
-        ADDEQ   r0, r0, #1
-        ADDNE   r0, r10, #1		; turn pointer into window handle
+        Rel     r0,r0,EQ
+        Rel     r0,r10,NE               ; turn pointer into window handle
 
         LDR     r1,rect_filters
 rect_filter_exit