implemented builtin noncopying slice

lib/system.nim

@@ -2620,7 +2620,7 @@ proc `[]=`*[Idx, T](a: var array[Idx, T], x: TSlice[int], b: openArray[T]) =
   if L == b.len:
     for i in 0 .. <L: a[i+x.a] = b[i]
   else:
-    sysFatal(EOutOfRange, "differing lengths for slice assignment")
+    sysFatal(EOutOfRange, "different lengths for slice assignment")
 
 proc `[]`*[Idx, T](a: array[Idx, T], x: TSlice[Idx]): seq[T] =
   ## slice operation for arrays. Negative indexes are **not** supported
@@ -2642,7 +2642,7 @@ proc `[]=`*[Idx, T](a: var array[Idx, T], x: TSlice[Idx], b: openArray[T]) =
       a[j] = b[i]
       inc(j)
   else:
-    sysFatal(EOutOfRange, "differing lengths for slice assignment")
+    sysFatal(EOutOfRange, "different lengths for slice assignment")
 
 proc `[]`*[T](s: seq[T], x: TSlice[int]): seq[T] = 
   ## slice operation for sequences. Negative indexes are supported.

lib/system/gc_ms.nim

@@ -313,6 +313,7 @@ proc mark(gch: var TGcHeap, c: PCell) =
       if not containsOrIncl(gch.marked, d):
         forAllChildren(d, waMarkPrecise)
   else:
+    # XXX no 'if c.refCount != rcBlack' here?
     c.refCount = rcBlack
     gcAssert gch.tempStack.len == 0, "stack not empty!"
     forAllChildren(c, waMarkPrecise)