Fix #446 (also #438): Wrong subapp response body handling and lost Content-Type header on mounted apps.
Release of 0.11.6 (bugfix)

Fix #446 (also #438): Wrong subapp response body handling and lost Content-Type header on mounted apps.
Fix: run() disabling debug mode.

Changed run(debug=*) default from False to None. None does not change the current mode.
Backported test case to make sure this release does not need the fix.
Fixed changelog