Modify the random distributions test to verify to 2 more decimal

Modify the random distributions test to verify to 2 more decimal
places of accuracy, but to allow +/- 1 units in the last (tested)
place.  This allows the test to pass on machines or with compilers
whose calculated values are off by epsilon from the expected results.
Because of the way the test is constructed, this was quite common and
often caused gratuitous test failures.

This is patch #5215, tested by Jason Stover and John Darrington.