Enhanced selection of default account in AccountManager

Ignore-this: 3197840470a13612e5921bb10965fd06

darcs-hash:20090318111229-1e3d8-2df475b71dc60b89cb8cd2ad306e2bc67d9d96a1
Made BonjourAccount's id a SIPAddress

Ignore-this: 8283aa085ae175bec2ef0940e571ef80

darcs-hash:20090318131740-1e3d8-4786d1b0a54d3bb5575b78f43cbe0b7310420a00