Updated fixtures to download 2-detector station data

This is important to catch bugs which only hit 2-detector stations, like
issue #39.  The download test datastore script is updated to only download
two days of data.
Fixed loss-of-precision bug.  Closes #39.

The loss of precision resulted from the fact that the pulseheights column
is an integer type.  Multiplying it in place truncates the floating point
numbers.  However, if you multiply it with a float and save the result in
*another* variable, the array is casted into a float, as desired.