Previously, some HTTP headers would not be transcribed to the WSGI
environment provided to applications. This could be happen if either:
* the header closely mirrors another CGI variable, such as
Request-Method or Path-Info, or
* the header closely mirrors a previous header but prefixed with
"Http-", such as Http-Foo when a Foo header has already been
received.
Now, only Content-Type and Content-Length will be skipped, and only
because they were previously already added as CONTENT_TYPE and
CONTENT_LENGTH keys.
https://github.com/eventlet/eventlet/pull/327