Bug Fixes - autofilter

- Auto filter now only creates a filter for read-only commands.
- Fixed bug whereby ambiguities were reported twice:
    "could be one of a, b, a, b".

src/Att.cpp

@@ -259,7 +259,6 @@ bool Att::validNameValue (
 
     std::string combined;
     join (combined, ", ", matches);
-    error += combined;
 
     throw error + combined;
   }