Create indexes using "tableName_columns" instead of "columns" as name.

This allows us to create different tables that have indexed fields with the same name.  For example a table `foo` with an indexed field `elvis`, and table `bar` also with an indexed field named `elvis`.  Before, qbs would try to name both indexes `elvis`, and fail trying to create the second one.  Now it will name them `foo_elvis` and `bar_elvis` respectively.