Disable NAT detection

Ignore-this: 9c8cdd7352fd08c33af144061102fab2

darcs-hash:20121211141203-b22ec-907b0bf4221500d433ab190d46b944699f919434
Use digits only for contact usernames to improve interoperability

Ignore-this: 463402ff791fc0af0deb87599292d733

darcs-hash:20121213131612-b22ec-7d7e4bec4b95f0ae927da84ecabe28ce90e88057