NEW_TIME_BASE: bolster date checking

[smwesten-usgs]

TSPROC fails to detect out-of-order dates when given values associated with the following sequence of dates (as supplied in an observation data *.ssf file):

05476000    6/1/2005    12:00:00    0.126
05476000    6/2/2005    12:00:00    0.137
05476000    3/23/2005    12:00:00    0.043
05476000    6/3/2005    12:00:00    0.083

The simulated values are supplied in another *.ssf file and look like this:

34_28  06/01/2005  12:00:00          0.1409
34_28  06/02/2005  12:00:00          0.1534
34_28  06/03/2005  12:00:00          0.1603
34_28  06/04/2005  12:00:00          0.1365

The resulting time series produced by TSPROC is:

s05476000et       06/01/2005   12:00:00    0.140900001    
s05476000et       06/02/2005   12:00:00    0.153400004    
s05476000et       03/23/2005   12:00:00   -0.734100223    
s05476000et       06/03/2005   12:00:00    0.160300002   

It appears that the negative value calculated in line 3 above is due to the fact that the routine attempts to linearly interpolate between data points, except in this case it is extrapolating to a point three months prior; the resulting value is problematic to say the least.