Improve error message generated in DataDrivenDBInputFormat when no splitter is available

Currently DataDrivenDBInputFormat will throw following exception in case that there is no available Splitter:

DBSplitter splitter = getSplitter(sqlDataType);
if (null == splitter) {
  throw new IOException("Unknown SQL data type: " + sqlDataType);
}

Text of the exception is very confusing as it's not describing what has actually happened. Would be great if this message would be improved by saying that Sqoop do not have splitter for given sql type and therefore user should either use different split column (argument --split-by) or lower number of mappers to 1 (splitters are not used in such case).