Implement krb5_get_init_creds_opt_set_change_password_prompt()

[spaceone]

To be compliant with MIT kerberos.
This function enables/disables prompting for a new password if the password of a user is expired.

[spaceone]

Ping.

[nicowilliams]

I had to make some minor whitespace changes, particularly for krb5_get_init_creds_opt_set_change_password_prompt() so that the make-protos tool could recognize it (otherwise warnings resulted). We don't seem to have any tests for password changing :( EDIT: No, we do have a test.

[spaceone]

Thank you for responding!

[nicowilliams]

Merged as 7422cd1.

[nicowilliams]

Thanks for the contribution!