added an option for delaysolver tool to select a single scan for processing (ACES-32)

git-svn-id: https://svn.atnf.csiro.au/askapsdp/trunk@6604 1db04d4c-0ff0-4329-ae0b-98c546476c6a
Perform row indexing in constant time rather (ASKAPSDP-1616)

Previous code used a triple nested summation, where the new code
used a sum of an arithmetic sequence which runs in constant time.


git-svn-id: https://svn.atnf.csiro.au/askapsdp/trunk@6605 1db04d4c-0ff0-4329-ae0b-98c546476c6a