* Add a gras_msgtype_dumpall() function to get the listing of all existing

* Add a gras_msgtype_dumpall() function to get the listing of all existing
  (registered) messages
* Change the semantic of gras_msgtype_by_name() to raise an error when not
  found
* Add a gras_msgtype_by_name_or_null() to retrieve the old semantic of
  gras_msgtype_by_name()
* Make sure that RPC callback do call gras_msg_rpcreturn() (and do so only
  once)

git-svn-id: svn+ssh://scm.gforge.inria.fr/svn/simgrid/simgrid/trunk@2909 48e7efb5-ca39-0410-a469-dd3cf9ba447f