Fix

Author: linasm

src/main/scala/scala/collection/decorators/MutableBitSetDecorator.scala

@@ -51,11 +51,7 @@ class MutableBitSetDecorator(protected val bs: mutable.BitSet) {
       val newSize = significantWordCount + wordOffset
       require(newSize <= MaxSize)
       ensureCapacity(newSize)
-      var i = newSize - 1
-      while (i >= wordOffset) {
-        bs.elems(i) = bs.elems(i - wordOffset)
-        i -= 1
-      }
+      System.arraycopy(bs, 0, bs, wordOffset, significantWordCount)
     } else {
       val revBitOffset = WordLength - bitOffset
       val extraBits = bs.elems(significantWordCount - 1) >>> revBitOffset