Modified SilenceableWaveFile to use a green model

Ignore-this: 4e5cbf6c3ff31d2ec3c9d5435085b41f

darcs-hash:20100111095833-1e3d8-7c1ba050044b52c43c6df53abcebcee50512ed1a
Made Account.credentials a property

Ignore-this: a7983f76838da8b1378e63d3ea0afc21

darcs-hash:20100111101854-1e3d8-f392d1e321b2c4e6681ee0b6c17a25bcf80b71e0