DateTime() doesn't create a fixed time object

The DateTime() method with no input args doesn't seem to initialize a structure to store the fixed time of "now" and instead appears to keep getting the current time.  This is not the expected behavior.

```
In [1]: from Chandra.Time import DateTime
In [2]: d = DateTime()
In [3]: d.secs
Out[3]: 530297635.8762741
In [4]: d.secs
Out[4]: 530297637.86023587
In [5]: d.secs
Out[5]: 530297639.47543186