Fix QueryParser regression with underscores in field names
Fix QueryParser regression with underscores in field names

During the StringIterator rewrite, I broke parsing of field names with
underscores. Fixes LUCY-269.

TODO: Add a test case.

apache/lucy,rbevers/lucy,pombredanne/apache-lucy,kidaa/lucy,kidaa/lucy,nwellnhof/lucy,pombredanne/apache-lucy,nwellnhof/lucy,rbevers/lucy,rbevers/lucy,rectang/lucy,apache/lucy,rbevers/lucy,rectang/lucy,apache/lucy,rbevers/lucy,kidaa/lucy,nwellnhof/lucy,rectang/lucy,rbevers/lucy,nwellnhof/lucy,kidaa/lucy,pombredanne/apache-lucy,nwellnhof/lucy,pombredanne/apache-lucy,pombredanne/apache-lucy,apache/lucy,kidaa/lucy,apache/lucy,kidaa/lucy,rectang/lucy,kidaa/lucy,kidaa/lucy,rectang/lucy,nwellnhof/lucy,rectang/lucy,pombredanne/apache-lucy,apache/lucy,rectang/lucy,rbevers/lucy,nwellnhof/lucy,pombredanne/apache-lucy,apache/lucy