Use optimal value for the echo canceller tail length

Ignore-this: 350376defede48c7e0c0b8ed19400812

darcs-hash:20130725122823-b22ec-41f3be3856a5edf8693b3399ba82a73777c24527
Removed no longer used code

Ignore-this: 5668e050f91c01b5ded39e697314bff3

darcs-hash:20130726110227-56b4d-e3bc2a5bacbffd4b62a4e881877ddda110f880ea