Add omitted namespace

[infostreams]

In the GetCalendarRequest and GetCalendarsRequest you use the {http://calendarserver.org/ns/:} namespace, but that one was not declared at the top of the XML document.

It's a superficial change only, the old code returns the same results from the CalDav server as the new code. However, the generated XML from the old code is somewhat quaint:

<?xml version="1.0" encoding="UTF-8"?>
<D:propfind xmlns:D="DAV:" xmlns:C="urn:ietf:params:xml:ns:caldav">
   <D:prop>
      <D:displayname />
      <D:resourcetype />
      <D:sync-token />
      <D:getetag />
      <x1:getctag xmlns:x1="http://calendarserver.org/ns/:" />
   </D:prop>
</D:propfind>

The new code generates

<?xml version="1.0" encoding="UTF-8"?>
<D:propfind xmlns:D="DAV:" xmlns:C="urn:ietf:params:xml:ns:caldav" xmlns:CS="http://calendarserver.org/ns/:">
   <D:prop>
      <D:displayname />
      <D:resourcetype />
      <D:sync-token />
      <D:getetag />
      <CS:getctag />
   </D:prop>
</D:propfind>