Support for Microsoft Set Password protocol

[Danilo Almeida]

Due to the interop issues, wouldn't is be simpler to just to have a
krb5_ms_set_password()?

My understanding is that everyone who needs the MS set password
functionality needs it only to manage Windows domains.  Therefore, they know
that they are talking to a Windows domain.  Hence, they want to make a call
that only does the MS thing.

If we want API cleanliness, we could have a krb5_set_password that takes a
flag of what flavor of set password to use.  For now, the only flavor would
be the MS flavor.  If we can eventually do a negotiate, we can have a
negotiate flavor.

- Danilo