The default behavior now preserves the 'content-type' header, at
the expense of not providing pseudo-streming in Safari, generic
WebKit, and older Chrome. Applications that require streaming
and already use 'prefer-stream' mode will not be affected.
The 'prefer-fast' mode is now deprecated, as that behavior now
matches the default. The 'allow-wrong-content-type' mode is new;
it gives the same behavior as the old default in case binary
streaming is essential.
Fixes#8
John Hiesey