This bug was caused when the chart encountered data outside of its
visible range (i.e., the upper bound of the array size). A test was
added that inserts some data from 2 years and 16 months in the past.
The test failed on the old version, throwing exactly the error in bug
report #1442.
The fix is to check whether or not the value is within the array range
before sending the "+=" operator. With this change, the test passes.
Also removing some instance variables that were never invoked in the
views. This sets up a future refactoring of the method of comptuting
rolling averages, which differs between the two types of "last year"
views being refactored.
