MXS-1249: Server version stored as uint64_t value

That allows the version to be updated and read atomically. If
major/minor/patch are stored as separate variables, you can get an
inconsistent set. Now it may be out of date by the time it is used,
but it will never be internally inconsistent.

include/maxscale/service.h

@@ -378,6 +378,6 @@ typedef enum service_version_which_t
  */
 void service_get_version(const SERVICE *service,
                          service_version_which_t which,
-                         SERVER_VERSION* version);
+                         uint64_t* version);
 
 MXS_END_DECLS