New constant

Author: michaelklishin

include/rabbit.hrl

@@ -146,6 +146,8 @@
 -define(ROUTING_HEADERS, [<<"CC">>, <<"BCC">>]).
 -define(DELETED_HEADER, <<"BCC">>).
 
+-define(EXCHANGE_DELETE_IN_PROGRESS_COMPONENT, <<"exchange-delete-in-progress">>).
+
 %% Trying to send a term across a cluster larger than 2^31 bytes will
 %% cause the VM to exit with "Absurdly large distribution output data
 %% buffer". So we limit the max message size to 2^31 - 10^6 bytes (1MB