Server: Fix grave misspelling of CONTENT_LENGTH wsgi variable (thx Honza Žerdík)

* Introduced in 5f2e50a0
* Caused the POST payload to be always ignored, breaking the function completely.
* Great job finding and debugging this, Honza Žerdík.

warden_server/warden_server.py

@@ -927,10 +927,10 @@ class Server(ObjectBase):
             # preserve compatibility with clients deployed in the wild, which use POST for
             # all requests (even those without payload, with no specified content length).
             # According to PEP3333, section "Input and Error Streams", the application SHOULD
-            # NOT attempt to read more data than specified by CONTENT-LENGTH. As stated in
-            # section "environ Variables", CONTENT-LENGTH may be empty (string) or absent.
+            # NOT attempt to read more data than specified by CONTENT_LENGTH. As stated in
+            # section "environ Variables", CONTENT_LENGTH may be empty (string) or absent.
             try:
-                content_length = int(environ.get('CONTENT-LENGTH', 0))
+                content_length = int(environ.get('CONTENT_LENGTH', 0))
             except ValueError:
                 content_length = 0