Require current password when using passwd to change your own password.

Add a new required parameter, current_password. In order to ask this
first I added a new parameter option, sortorder. The lower the value the
earlier it will be prompted for.

I also changed the way autofill works. It will attempt to get the default
and if it doesn't get anything will continue prompting interactively.

Since current_password is required I'm passing a magic value that
means changing someone else's password. We need to pass something
since current_password is required.

The python-ldap passwd command doesn't seem to use the old password at
all so I do a simple bind to validate it.

https://fedorahosted.org/freeipa/ticket/1808

ipalib/frontend.py

@@ -777,6 +777,8 @@ class Command(HasParam):
         self._create_param_namespace('options')
         def get_key(p):
             if p.required:
+                if p.sortorder < 0:
+                    return p.sortorder
                 if p.default_from is None:
                     return 0
                 return 1