Space binner OCTS updates

Changes were made to the spacebin processing for OCTS, which were applicable to SeaWiFS. The changes are:

1. to use the file mid-time, rather than the start time, and
2. to use the actual dataday duration, instead of assuming 24 hours, when determining whether a given scene should overlap with the preceding or following dataday.

These changes eliminated occasional failures of the spacebin program for OCTS Level-2 scenes, and also provide benefits for SeaWiFS.

The failures occur during the winter, for orbits which are close to 12:00 UTC. An example of this can be seen in the daily mapped chlorophyll products for January 10, 2002 (below). In this image, the binning failure for one GAC orbit results in a lack of binned data in the Mediterranean Sea and the South Atlantic region near the center of the file.

The same day was reprocessed with the modified spacebin (second image below). This image shows that all GAC orbits were successfully binned for that day.