Index: translate/storage/base.py
===================================================================
--- translate/storage/base.py	(revision 7803)
+++ translate/storage/base.py	(working copy)
@@ -297,6 +297,34 @@
         """This unit in a list."""
         return [self]
 
+    def setprev_source(self, source):
+        """Sets the previous source message for this unit"""
+        pass
+
+    def getprev_source(self):
+        """Gets the previous source message for this unit"""
+        pass
+
+    prev_source = property(getprev_source, setprev_source)
+
+    def setprev_context(self, context):
+        """Sets the previous context of this unit"""
+        pass
+
+    def getprev_context(self):
+        """Gets the previous context of this unit"""
+        pass
+
+    prev_context = property(getprev_context, setprev_context)
+
+    def set_as_previous(self):
+        """Sets this unit as a previous unit message"""
+        if self.isfuzzy():
+            return
+        self.setprev_context(self.getcontext())
+        self.setprev_source(self.source)
+        self.markfuzzy()
+
     def buildfromunit(cls, unit):
         """Build a native unit from a foreign unit, preserving as much  
         information as possible."""