tests/: Add basic iCal import tests

Tests ical-002.sh and ical-003.sh currently fail due to bugs in duration
and exception parsing.

Reported-by: Håkan Jerning <jerning@home.se>
Signed-off-by: Lukas Fleischer <calcurse@cryptocrack.de>
io.c: Remove superfluous space from message

Signed-off-by: Lukas Fleischer <calcurse@cryptocrack.de>
ical.c: Simplify and fix ical_durtime2long()

Correctly parse all types of durations. Before this change, durations
without an hour or minute component were not parsed properly.

Reported-by: Håkan Jerning <jerning@home.se>
Signed-off-by: Lukas Fleischer <calcurse@cryptocrack.de>
ical.c: Parse multiple exception rules properly

There can be multiple EXDATE lines per event. Parse them correctly
instead of making the last line overwrite the previous ones.

Reported-by: Håkan Jerning <jerning@home.se>
Signed-off-by: Lukas Fleischer <calcurse@cryptocrack.de>