#25 mstore generates non-unique event IDs

[Mark Schonbach]

The mstore driver uses the time(NULL) function to
generate event IDs. If more than one event is added to
the calendar within one second, those events will have
the same event ID.

I have created a patch which corrects the problem by
including part of the microsecond in the ID.

[Mark Schonbach]

diff for mstore.c