fixed a rdonly flag bug in moo_shallowcpy()

added SequenceableCollection>>swap:with:

moo/kernel/Apex.moo

@@ -112,6 +112,8 @@ extend Apex
 	## -------------------------------------------------------
 	method(#dual,#primitive,#lenient) _shallowCopy.
 	method(#dual,#primitive) shallowCopy.
+	method(#dual,#primitive,#lenient) _copy. ## alias to _shallowCopy
+	method(#dual,#primitive) copy. ## alias to shallowCopy
 
 	## -------------------------------------------------------
 	## -------------------------------------------------------

moo/kernel/Collect.moo

@@ -110,6 +110,17 @@ class SequenceableCollection(Collection)
 
 		startIndex to: stopIndex do: [:i | aBlock value: (self at: i) value: i].
 	}
+
+	method swap: anIndex with: anotherIndex
+	{
+		## the subclass must implement at: and at:put for this to work.
+
+		| tmp |
+		tmp := self at: anIndex.
+		self at: anIndex put: (self at: anotherIndex).
+		self at: anotherIndex put: tmp.
+	}
+
 }
 
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