MGR: eliminate almost all overhead from my commit a8cc13f unless assistive software is in use

clientgui/mac/MacAccessiblity.mm

@@ -1047,6 +1047,8 @@ static void wxRectToNSRect(wxRect &wxr, NSRect &nsr) {
 // is somewhere in the caller chain.
 // I wish I could find a more efficient way to do this.
 //
+static BOOL AccessibilityEnabled = false;
+
 - (NSView *)hitTest:(NSPoint)aPoint {
     // [NSThread callStackSymbols] is not available in OS 10.5, so 
     // BOINC does not fully implement accessibility under OS 10.5.
@@ -1073,7 +1075,8 @@ static void wxRectToNSRect(wxRect &wxr, NSRect &nsr) {
         return [super hitTest:aPoint];  // Point is not within our rect
     }
 
-//    NSArray *theStack = [NSThread callStackSymbols];
+    if (AccessibilityEnabled) {
+    //    NSArray *theStack = [NSThread callStackSymbols];
         NSArray *theStack = [ NSThread performSelector:@selector(callStackSymbols) ];
         
         int limit = [ theStack count ];
@@ -1094,12 +1097,14 @@ static void wxRectToNSRect(wxRect &wxr, NSRect &nsr) {
             }
             ++i;
         } while (i < 15);
+    }
     
     return [super hitTest:aPoint];  // Not an accessibility call
 }
 
 
 - (BOOL)accessibilityIsIgnored {
+    AccessibilityEnabled = true;
     return NO;
 }