Generated records should allow toString() that does not append end-of-record delimiter

The SqoopRecord.toString() and SqoopRecord.toString(DelimiterSet) methods always append an end-of-record delimiter. Sqoop uses its own OutputFormat when rendering these to text files, so that the user's delimiters are preserved.

Other users could use this OutputFormat when working with SqoopRecord instances in their own MapReduce code, but it would also be nice to "play nice" with TextOutputFormat in the event that the intent is newline-terminated records.

This patch allows users to suppress end-of-record delimiter generation when formatting records with toString.