Fix bug with multiline values

The URL that showed this error up was

https://mozorg.cdn.mozilla.net/media/caldata/GermanHolidays.ics

with the following entry:

BEGIN:VEVENT
CREATED:20061023T132503Z
LAST-MODIFIED:20101214T141313Z
DTSTAMP:20101214T141313Z
UID:917544590
SUMMARY:Heilige drei Könige
STATUS:CONFIRMED
RRULE:FREQ=YEARLY;BYMONTH=1
CATEGORIES:Feiertag
DTSTART;VALUE=DATE:20060106
DTEND;VALUE=DATE:20060107
DESCRIPTION:Christlicher Feiertag. Nur in Baden-Württemberg\, Bayern und
 Sachsen-Anhalt.
X-MOZ-GENERATION:1
END:VEVENT

tests/storage/test_http.py

@@ -24,6 +24,7 @@ class TestHttpStorage(object):
             (u'BEGIN:VEVENT\n'
              u'SUMMARY:Eine zweite Kurzinfo\n'
              u'DESCRIPTION:Beschreibung des anderen Termines\n'
+             u' With an extra line for description\n'
              u'BEGIN:VALARM\n'
              u'ACTION:AUDIO\n'
              u'TRIGGER:19980403T120000\n'

vdirsyncer/storage/http.py

@@ -20,7 +20,8 @@ def split_collection(text):
     collection_type = None
     item_type = None
     for line in text.splitlines():
-        if not line.strip():
+        if u':' not in line:
+            item.append(line)
             continue
         key, value = (x.strip() for x in line.split(u':', 1))
         if key == u'BEGIN':