tweaks for date_ical_escape_text to make it closer to ical spec conformance

Attached is a patch that makes 2 changes to the date_ical_escape_text function to make it more ical spec conformant.

The first changes the escape of all \ characters to only those that are on a word boundary. \n as a litteral (not "\n" but a slash and an n in the text) in ical should remain as such, as it is how new lines are encoded. The previous escaping was creating a \\n which broke newlines.

The second change adjusts the wrapping and indenting of multiline blocks from using "\n " to using "\r\n ". The spec requires "\r\n" for new lines on multiline blocks, and ical generated without them fails the ical validator here (http://severinghaus.org/projects/icv/).

I'm using these two changes on http://mhvlug.org for our calendar to get better ical out of the system, and it would be great if these got upstreamed. Feedback is appreciated.