Bug #56767: Make sure client plugins in 1054 are compatible with

connectors plugins
      
Implemented changes needed to keep the client plugin API compatible with 
the existing plugins :
      
1. Provided an options() client plugin API to let the application pass
options to the plugin after loading it
2. Added "License" (const char *) to specify the client plugin's license
3. Added "mysql_api" as a placeholder that the client library can use
to pass function pointers to the plugin so that the plugin can call the 
C lib back.
4. Updated the existing client plugins to comply with the API change.
5. Added more detailed error message generation for Windows.

plugin/auth/dialog.c

@@ -319,8 +319,11 @@ mysql_declare_client_plugin(AUTHENTICATION)
   "Sergei Golubchik",
   "Dialog Client Authentication Plugin",
   {0,1,0},
+  "GPL",
+  NULL,
   init_dialog,
   NULL,
+  NULL,
   perform_dialog
 mysql_end_client_plugin;
 

plugin/auth/test_plugin.c

@@ -196,6 +196,9 @@ mysql_declare_client_plugin(AUTHENTICATION)
   "Georgi Kodinov",
   "Dialog Client Authentication Plugin",
   {0,1,0},
+  "GPL",
+  NULL,
+  NULL,
   NULL,
   NULL,
   test_plugin_client