Bad table name on master_create_distributed_table()

This fix handles when master_create_distributed_table is called with
a an index as the first argument. More generally, it is called with
a relation that is not ordinary table or foreign table.

closes #13 
Since `char *` is such a common C type, we don't include it in the variable name: `tableName` is sufficient. If a function has both a `text *` and `char *` representation of a given variable, we probably do: `tableNameText` for the `text *` and just `tableName` for the `char *` one.