Working HTTP transport.

This uses base64 encoding and POST requests to encapsulate kerberos messages.
Configuration file syntax changed to `kdc =
[(tcp|udp|http)://]<addr.of.kdc>[:<port>]`.
Enable kpasswd protocol to use HTTP for transport.

Currently, if the other end of the HTTP proxy is not running on (effectively)
the same machine as the KDC, the result will be "kpasswd: Incorrect net
address changing password".
Add ability to POST to a specific page for HTTP transport.

krb5.conf syntax is now `kdc =
[(tcp|udp|http)://]<addr.of.kdc>[:<port>][/<page>]` with the understanding
that <page> will be ignored when HTTP is not specified.
Add HTTPS transport for Kerberos traffic.

krb5.conf syntax is now `kdc =
[(tcp|udp|http|https)]://<addr.of.kdc>[:<port>][/<page>]` with the
understanding that <page> will be ignored if the protocol is not HTTP or
HTTPS.