Replace asSearchTextExpression implementations with _asSearchTextExpression and a default asSearchTextExpression wrapping _asSearchTextExpression call.
This fixes unneeded parentheses in generated search text expressions.


git-svn-id: https://svn.erp5.org/repos/public/erp5/trunk@27662 20353a03-c40f-0410-a6d1-a30d3c3de9de