SU2Proxy support is enabled when GssapiUseS4U2Proxy is set to On
When S4U2Proxy is enabled GssapiDelegCcacheDir is used to determine
where delegated credentials are stored. The ccache type used is always
of type FILE and is located in the provided directory (defaults to /tmp).
The credentials are stored in a file named after the client credentials
so the directory SHOUL NOT be world writeable if a mutiuser system is
used as ccache file names are predictable.

Keys (encryption+MAC) can now be stored in apache configuration.
The key must be a base64 encoded blob of original length of 32 bytes
(16 bytes for encryption and 16 for the MAC key)

The format is:
key:<base64 blob>

By setting GssapiUseSessions we enable the module to store a bearer
token with the user and gss names in the client, this way we can allow
clients to perform authentication once but then remain authenticaed
for the duration of the session or until the original credentials expire.

The Secure cookie used to store the token is encrypted using a randomly
generated AES key at process startup. This means multiple apache servers
will not be able to use the same cookie, however the client will reauth
transparently if the cookie cannot be read.

Move all includes into it and also include config.h which was missing
causing some ifdefed code not to be compiled.
Also address includes conflict between httpd.h and config.h and the
PACKAGE_* variables.

Remove unnecessary cruft, that was only making things harder to read.

On my system I have high UIds, without tar-pax make dist fails.
Also add other useful parameters

This way the context is available for the duration of the connection.
It is also properly freed if the connection is interrupted before the context
is fully established.

On errors mc->ctx would be left pointing at the freed context,
make sure it is cleared if we delete the context.