Add skeletal implementation of keysSortyedByValue*** methods

Headers/Foundation/NSArray.h

@@ -283,7 +283,7 @@ DEFINE_BLOCK_TYPE(GSPredicateBlock, BOOL, GS_GENERIC_TYPE(ElementT),
 - (GS_GENERIC_CLASS(NSArray, ElementT) *)
     sortedArrayWithOptions: (NSSortOptions)options
            usingComparator: (NSComparator)comparator;
-
+  
 /**
  * Performs a binary search of the array within the specified range for the
  * index of an object equal to obj according to cmp.

Headers/Foundation/NSDictionary.h

@@ -109,6 +109,8 @@ DEFINE_BLOCK_TYPE(GSKeysAndObjectsPredicateBlock, BOOL,
 #endif
 
 - (GS_GENERIC_CLASS(NSArray,ValT)*) keysSortedByValueUsingSelector: (SEL)comp;
+- (GS_GENERIC_CLASS(NSArray,ValT)*) keysSortedByValueUsingComparator:(NSComparator)cmptr;
+- (GS_GENERIC_CLASS(NSArray,ValT)*) keysSortedByValueWithOptions:(NSSortOptions)opts usingComparator:(NSComparator)cmptr;  
 - (GS_GENERIC_CLASS(NSEnumerator,ValT)*) objectEnumerator;	// Primitive
 - (GS_GENERIC_TYPE(ValT)) objectForKey:
   (GS_GENERIC_TYPE(KeyT))aKey;				// Primitive

Source/NSArray.m

@@ -1219,7 +1219,6 @@ compare(id elem1, id elem2, void* context)
   return NSNotFound;
 }
 
-
 /**
  * Returns a string formed by concatenating the objects in the receiver,
  * with the specified separator string inserted between each part.

Source/NSDictionary.m

@@ -949,6 +949,20 @@ compareIt(id o1, id o2, void* context)
   return k;
 }
 
+- (NSArray *)keysSortedByValueUsingComparator:(NSComparator)cmptr
+{
+  return [self keysSortedByValueWithOptions:0 usingComparator:cmptr];
+}
+
+- (NSArray *)keysSortedByValueWithOptions:(NSSortOptions)opts usingComparator:(NSComparator)cmptr
+{
+  //return [[self allKeys] sortedArrayWithOptions:opts
+  //                             usingComparator:^NSComparisonResult(id key1, id key2) {
+  // return cmptr([self objectForKey:key1], [self objectForKey:key2]);
+  //}]
+  return nil;
+}
+
 /**
  *  Multiple version of [-objectForKey:].  Objects for each key in keys are
  *  looked up and placed into return array in same order.  For each key that