Use plist API to write the plist

[stuart.morgan, 2008-12-06 20:42:15]

I figured that rather than doing XML escaping ourselves, we should just make absolutely sure that we are always making a valid plist, so we aren't fixing another edge case in the next release. It's a bit less straightforward, but I think the safety is worth it. The only change in what it writes is that PrincipalURL is no longer using the unescaped ident. Note that the old code confusingly referred to the unescaped version as "encodedIdent", where ident corresponded to ENCODED_EMAIL and encodedIdent (which should have been called unescapedIdent) corresponded to EMAIL.

[TVL, 2008-12-07 05:24:16]

lgtm