This task constructs RGS event-selection regions. It reads an event
list processed by rgsfilter
and modifies a source list
created by rgssources. Flag columns in the SRCLIST
table determine which regions are added to the source list. This task
should be run any time the existing set of regions gets out of date.
Existing regions are replaced only as necessary. As a convenience,
this task may also be used to edit the flag columns in the
SRCLIST table.