Add some configure bits for GSS-API

rxgk will require gss_pseudo_random and might want a couple other
krb5-specific bits.  We'll also need substvars to tell whether or
not we can try building these things.

Change-Id: Id18eb3f554605875696095eb40c25ec54df1f74b
Add rxgk boilerplate

Error table, protocol description, and stubs for the security object
routines, with header to declare them.

The public header rxgk.h currently only contains a few typedefs and the
NewSecurityObject prototypes, and includes the RPC interface and com_err
code headers.

Change-Id: I7893f78119bb4aef12112cc1e51e1ec69de326c2
Dummy Makefile for rxgk

Include a libtool export symbol list for the shared library, which
only exports the client RPC calls for now.

Also connect the rxgk directory up to be buildable from the root, but
nothing depends on it yet so it will not be built.
Configure glue for rxgk

Add an --enable-rxgk switch to control whether the feature is used.
For now, just build the code as a dependency of finale, but we will
phase it in to other parts of the tree as appropriate.

We want to always build as much code as we can to benefit from the
automated build testing, so build rxgk if there is an appropriate
GSSAPI library available, but do not install anything unless the
configure argument was given.

Change-Id: Iab661d47aac77c1a238e809362015b869752df18
Add rxgk_crypto_rfc3961.c

rxgk wrappers around an external crypto library, in this case, our
in-tree rfc3961 library.  Primitives for encryption/decryption and
MIC/VerifyMIC, ways to generate and free rxgk_key objects, etc..

Change-Id: I7525086043baf54f5c3019b3f5ab3495760c4236
Add RXGK_NOW()

A quick routine to get the current timestamp.

Change-Id: I0051b5c8e5ad61e35431d97454bf2741daba90cb
Add rxgk_token.c

Routines for constructing tokens (both regular and printed), and
helpers.

Change-Id: I0cde7fd0cdf9a27777523cd502b21bdccef41dcc
Add rxgk_gss.c

All the routines which deal with GSSAPI types.
This is, in practice, how the client gets a token, and the server
backend for GSSNegotiate().

Change-Id: Id2966de07853dd6a74cb40225851728d2422421c