change REPL DUMP syntax to use "LIMIT" instead of "BATCH" keyword

Currently, REPL DUMP syntax goes:

REPL DUMP [<dbname>[.<tblname>]] [FROM <eventid> [BATCH <batchSize>]]

The BATCH directive says that when doing an event dump, to not dump out more than batchSize number of events. However, there is a clearer keyword for the same effect, and that is LIMIT. Thus, rephrasing the syntax as follows makes it clearer:

REPL DUMP [<dbname>[.<tblname>]] [FROM <eventid> [LIMIT <maxEventLimit>]]