Gracefully parse iCal parameters with colons

According to RFC 5545, iCalendar content lines can have optional
parameters, which can be quoted strings containing colons (":"). Make
sure that such colons are not interpreted as delimiters marking the
start of the value string.

Also, add a test case that covers this corner case.

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

test/Makefile.am

@@ -49,6 +49,7 @@ TESTS = \
 	ical-005.sh \
 	ical-006.sh \
 	ical-007.sh \
+	ical-008.sh \
 	next-001.sh \
 	search-001.sh \
 	bug-002.sh \