Close Issue #18
use mechanism to resolve calendar-URIs described in
http://code.google.com/p/sabredav/wiki/BuildingACalDAVClient#Discovery
Change calendar detection
- first check entered URL is an calendar (Yahoo doesn't list Calendars
in calendar-home-set)
- Log outputs with confidential information (urls and username) only in
BuildConfig.Debug-Mode
- clean StringBuilder on startElement
- clear currentElement on endElement
Revert "- clean StringBuilder on startElement - clear currentElement on endElement"

This reverts commit 875268a475acaef00363b2714ab4a2a24f390a3a.
Signed-off-by: gege <gege@gege.org>
Merge branch 'patch_david'
Correct David patch for davical

Signed-off-by: gege <gege@gege.org>