allow duplicate headers in http router
prepare for 2.0.4
Fix some bugs introduced in c57baae4775f4e665b7e158582234ac558a2bf7b preventing the 'mime' routing function from working with request variables, and actually return the found mimetype

The uwsgi_route_var_mime function had two errors preventing it from (afaics ever) working:
 1. Redefine the 'ret' variable inside an if block. This meant that if the uwsgi_get_mime_type function ever actually found a matching mimetype, the length of the matching value would be corectly set, but the function returns NULL (the value of the function-level ret variable)
 2. The function was looking up the request variable correctly, BUT then passing in the raw config string to uwsgi_get_mime_type NOT the resolved varible value, making the lookup just a waste of cycles.
Merge pull request #585 from stestagg/master

Fix uwsgi_route_var_mime
fix headers parsing in http router