Usage: InFileNm1 InFileNm2 [OutFileNm]
Where: InFileNm1 and InFileNm2 are processed to produce OutFileNm
such that OutFileNm contains all lines from InFileNm2 which were
inserted (vis-a-vis InFileNm1.
In other words, if InFileNm2 is assumed to be a newer version
of InFileNm1 with changed, OutFileNm contains all lines which were
inserted into InFileNm1 to create InFileNm2.
Default OutFileNm is Std Output.
InFileNm1 and InFileNm2 are assumed to be sorted in ASCII sequence.