Add aresult variable for CALENDAR_WRITE

This patch adds a CALENDAR_SUCCESS=1/0 variable that is set to show whether or
not CALENDAR_WRITE has passed. This patch also adds some debugging for caldav
PUT responses and no longer treats responses with no body as an error (as a PUT
gets a 201 Created with no body).

(closes issue ASTERISK-16903)
Reported by: Clod Patry
Tested by: Terry Wilson
Patches:
  	calendarstatus.diff uploaded by Clod Patry (License #5138), slightly modified by Terry Wilson

Review: https://reviewboard.asterisk.org/r/1692/
- This line, and those below, will be ignored--

M    res/res_calendar.c
M    res/res_calendar_exchange.c
M    res/res_calendar_caldav.c


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@352916 65c4cc65-6c06-0410-ace0-fbb531ad65f3