HTML form variable 'summary' was used in two

HTML form variable 'summary' was used in two
different places: for the summary description of a calendar
event, and for a flag to tell the message reading loop to
display a mailbox summary view.  As a result, if an event
summary began with a number, and the number was not zero,
the flag would be set, causing a mailbox summary to appear
instead of the calendar after save/cancel.   Renamed the
latter variable to 'is_summary' to remove the conflict.