Add ntlm_auth, a new program to provide a stable interface to winbind's

Add ntlm_auth, a new program to provide a stable interface to winbind's
authentication code.

In particular, ntlm_auth is designed to replace the winbind authentication
'helpers' currently supplied by Squid.  I have added support for the current
plaintext password protocol used by Squid, and will add the real guts (NTLMSSP
support) shortly.

I'll merge this into 3.0 when I've got the interface more stable (error message
format etc) and got the important NTLMSSP support added.

Also move SWAT's URL decoding code into util_str.c, for use in both utilities.

Andrew Bartlett