The parser rule for expressions in a udf parameter list contains 
two hacks: 
First, the parser input stream is read verbatim, bypassing 
the lexer.
Second, the Item::name field is overwritten. If the argument to a
udf was a field, the field's name as seen by name resolution was
overwritten this way.
If the field name was quoted or escaped, it would appear as e.g. "`field`".
Fixed by not overwriting field names.