Time Agg Series Slot Config: Skip intervals containing NaNs [6036] [4]
Bug Number: n/a
Release notes (y/n): No (not this detail)
For Release Nums: 7.2

A third aggregation option was added (presented as the second of three 
choices) for the treatment of NaNs (or NaNs and Output values):

   "Do not aggregate intervals having NaN/Output values".

The target timesteps in the aggregated series slot of such intervals are 
assigned NaN.

Changes made today, recognizing these two nuances:

  (1) The "Synchronize Objects with New Timestep" aggregation function 
      options offer special handing of NaN-or-Output values, whereas the 
      Time Aggregation Series Slot aggregation function options offer 
      special handling for only NaN values.

  (2) With the "First" and "Last"* aggregation functions, series slot 
      timesteps having NaNs and Output values in timesteps other than 
      those (the first or last timestep in each aggregation interval) 
      should not effect the operation of the new option.

Current screenshots:
http://cadswes2.colorado.edu/~philw/2017/bugs/6036/2017-12-12/SetRunTimestepAction2.png
http://cadswes2.colorado.edu/~philw/2017/bugs/6036/2017-12-12/SynchronizeTimestepChangeDlg3.png
http://cadswes2.colorado.edu/~philw/2017/bugs/6036/2017-12-12/TimeAggSerSlotConfig3.png

Note: There is a pre-existing bug with the "Error on NaN" choice when the 
"First" or "Last"* aggregation function is selected.  Only one value in the 
source interval should be considered (i.e. the first or last), but we are 
generating an error if a NaN is encountered in some other timestep.  This 
preexisting problem isn't related to the introduction of the new "Do not 
aggregate intervals having NaN values" option, so I'm going to proceed with 
this code change, and file a bug for that problem.  DETAIL: The problem is 
that this condition is detected in the source timestep iteration in method 
SeriesSlot::TimeAggSpec::recomputeOwnerSlot(), but needs to be moved down 
to computeAggSlotValue() or the aggregation function helper functions 
called from that method.

*Note that "Last" is the implicit aggregation function for aggregation in 
the "Synchronize Timestep Change" operation when changing the model timestep 
size, e.g. from daily to monthly -- FOR VOLUME UNITS.