Fix and test gauges

This is modification for the previous pull request issue_184_fix. Renamed the branch because
the modifications here are not relevant to issue 184 :). Mainly related to issue 190. This branch includes:
* Adding a test for gauges.
* Add the capability of keeping gauges in memory
* Fix for calculating gauges indices (still fail in 9 process run)
* Modified the utility function check_diff:
      - Now it handles arrays as input
      - I've modified its output because in case of arrays, I thought it is not useful to print the whole array (please tell me if you think this should be modified)