logilab-database #77769 process_cursor method [validation pending]

Currently, there is a process_result method on a lgd.dbapi_module that processes a resultset row and applies, if needed, transformations such as str->unicode, int->bool, etc. It's a very fine-grained method and having a more high-level one to process all the rows as once would allow to memorize which transformations are needed for a given column and optimize processing on large result sets.