Inclusion of 'content-encoding: deflate' header now (really) happens
per request, and not "per state" (where any request got this header
appended and broke those unaware requests that didn't compress their
data.)
The "Content-Encoding: deflate" header is now added from
within the compression routine itself, and _not_ from the
"exchange handle".
This fixed the bank-lib functions as those do not use any
exchange handle, and therefore were wrongly sending compressed
bodies without adding the mentioned HTTP header.
