[etwist] use more specific REQUEST_ENTITY_TOO_LARGE instead of BAD_REQUEST
When a request body exceeds the configured limit, return 413 to the
client instead of a generic 400.
if versions_map['cubicweb'][0] == (3, 7, 4):
config['http-session-time'] *= 60
config['cleanup-session-time'] *= 60
config['cleanup-anonymous-session-time'] *= 60