Improvements that were discussed with Tomas.

Maintain protocol backwards/forwards compatibilty for client and server and support
the commands from ndb_mgm 'as expected'


ndb/include/mgmapi/mgmapi.h:
  Add ndb_mgm_stop3 mgmapi function.
   - This supports stopping all DB nodes, or all DB and MGM nodes.
   - It also returns to mgmapi program if it needs to disconnect to apply changes.
  
  Add ndb_mgm_restart3 mgmapi function.
   - Tells mgmapi program if it needs to disconnect to apply changes
  
  Add (internal) ndb_mgm_get_version
   - designed to be used to find out what protocol version we need to speak to the server.
ndb/src/mgmapi/mgmapi.cpp:
  Add cache of mgmd version to ndb_mgm_handle. Only filled out in functions that
  need to know the version of the mgmd we're talking to.
  Initialize these members in create handle.
  added ndb_mgm_get_version which asks the mgm server what version it is. This call
  has been supported since the dawn of time, no compatibility issues here.
  
  Add implementation of ndb_mgm_stop3
  Check what version of the protocol the server speaks, and speak it.
  Add compatibility for ndb_mgm_stop2
  
  Same for ndb_mgm_restart3.
ndb/src/mgmclient/CommandInterpreter.cpp:
  Simplify stop and restart code.
  
  Use the new ndb_mgm_(stop|restart)3 calls to find out if we need to disconnect.
ndb/src/mgmsrv/MgmtSrvr.cpp:
  Add nice call for shutting down MGM servers (like shutdownDB)
ndb/src/mgmsrv/MgmtSrvr.hpp:
  add prototype for shutdownMGM
ndb/src/mgmsrv/Services.cpp:
  Add restart node v2, stop v2, stop all v2 while maintaining protocol backwards
  compatibility.
  
  Unfortunately we can't add result lines due to protocol errors in clients :(
  Neither can we add extra things to the 'result: Ok' line due to the use of
  strcmp instead of strncmp.
ndb/src/mgmsrv/Services.hpp:
  Add prototypes for restart, stop and stopall v1 and v2