Bug #59489 Enable setting of env. variables for mysqld from mtr

Added --mysqld-env option, propagate via safe_process
Simplified: should be safe to set in parent safe_process after it's started
Addendum: catch cases of --mysqld-env w/o value, assume env.var 
    name never begins with "--"

mysql-test/lib/My/SafeProcess/safe_process_win.cc

@@ -1,4 +1,4 @@
-/* Copyright (C) 2008 MySQL AB, 2009 Sun Microsystems, Inc.
+/* Copyright (c) 2008, 2011, Oracle and/or its affiliates. All rights reserved.
 
    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
@@ -220,6 +220,10 @@ int main(int argc, const char** argv )
       {
         nocore= TRUE;
       }
+      else if ( strncmp (arg, "--env ", 6) == 0 )
+      {
+	putenv(strdup(arg+6));
+      }
       else
         die("Unknown option: %s", arg);
     }