Declare a nominal package dependency on org
Deal with UIDs which are longer than one line.

(org-caldav-rewrite-uid-in-event): Move UID extraction into
`org-caldav-get-uid' and deal with UIDs which reach over several
lines.
Restore UID rewriting which was broken in last commit.

(org-caldav-rewrite-uid-in-event): Actually rewrite the UID in the
buffer.
(org-caldav-update-eventdb-from-org): Use it.
Fix double-entry error reporting.

(org-caldav-update-eventdb-from-org): Add calendar-id to
`org-caldav-sync-result' when adding double-entry error.
Fix org-cleanup-ics-description timestamp removal
Reset `org-caldav-empty-calendar' when switching calendars.

(org-caldav-sync-calendar): `org-caldav-empty-calendar' needs to be
reset on switching to another calendar.
Merge pull request #41 from purcell/patch-1

Declare a nominal package dependency on org
Copyright
Allow to override any org variables in org-caldav-calendars.

(org-caldav-var-for-key): As default, prefix key with "org-".
(org-caldav-calendars): Document the above.