[MERGE][1.3.1][#208418] Return the correct knit serialisation method in _StreamAccess

[Robert Collins]

Robert Collins has voted tweak.
Status is now: Conditionally approved
Comment:
+            orig_options = 
list(self.backing_index.get_options(version_id))
+            if 'fulltext' in orig_options:
+                pass
+            elif 'line-delta' in orig_options:
+                # Texts from the backing knit are always returned from 
the stream
+                # as full texts
+                orig_options.remove('line-delta')
+                orig_options.append('fulltext')
+            else:
+                raise errors.KnitIndexUnknownMethod(self, options)
+            return orig_options


That looks like a list-aliasing bug waiting to happen. Better to create 
a new options tuple I think.

For details, see: 
http://bundlebuggy.aaronbentley.com/request/%3C20080404070508.GA20605%40steerpike.home.puzzling.org%3E