WL#2678: Support catalog names in identifiers

In order to support queries built using the metadata that may current report the 
catalog as 'def', we should add support in the parser for catalogs and simply 
throw an error for any catalog other than 'def'. For example:

  SELECT * FROM def.mysql.user;

  SELECT def.mysql.user.Host FROM def.mysql.user;

"def" is the catalog name currently returned in sql/protocol.cc.

This would be a precursor to WL#942, which is real Catalog support.