Rename max_document_size to max_http_request_size

`max_document_size` is implemented as `max_http_request_size`. There was no
real check for document size. In some cases the implementation was close enough
of a proxy (PUT-ing and GET-ing single docs), but in some edge cases, like
_bulk_docs requests the discrepancy between request size and document size
could be rather large.

The section was changed accordingly from `couchdb` to `httpd`. `httpd` was
chosen as it applies to both clustered as well as local interface.

There is a parallel effort to implement an actual max_document_size check. The
set of commit should be merged close enough together to allow for a backwards
compatible transition.

COUCHDB-2992

src/chttpd.erl

@@ -629,8 +629,8 @@ body(#httpd{mochi_req=MochiReq, req_body=ReqBody}) ->
     case ReqBody of
         undefined ->
             % Maximum size of document PUT request body (4GB)
-            MaxSize = list_to_integer(
-                config:get("couchdb", "max_document_size", "4294967296")),
+            MaxSize =  config:get_integer("httpd", "max_http_request_size",
+                4294967296),
             Begin = os:timestamp(),
             try
                 MochiReq:recv_body(MaxSize)

src/chttpd_external.erl

@@ -93,7 +93,7 @@ json_req_obj_field(<<"headers">>, #httpd{mochi_req=Req}, _Db, _DocId) ->
     Hlist = mochiweb_headers:to_list(Headers),
     to_json_terms(Hlist);
 json_req_obj_field(<<"body">>, #httpd{req_body=undefined, mochi_req=Req}, _Db, _DocId) ->
-    MaxSize = config:get_integer("couchdb", "max_document_size", 4294967296),
+    MaxSize = config:get_integer("httpd", "max_http_request_size", 4294967296),
     try
         Req:recv_body(MaxSize)
     catch exit:normal ->