Disconnect the texinfo admin guide from the build

Its content has been migrated to or superseded by the reST documentation,
essentially entirely in krb_admins.

A few portions of the texinfo document are simply no longer relevant
and do not need to be migrated.  In particular:
Information about reporting bugs lives on k5wiki.kerberos.org.
General Kerberos concepts/introduction will be elsewhere in the tree.
We do not need to document the time zones accepted by kadmin.
We do not need a table of the various error codes and strings in our
formal documentation.
A complete description of the layout of our source tree is not useful
or relevant to most Kerberos administrators.

ticket: 7408
Remove make glue for texinfo admin guide

Towards removing the texinfo docs entirely.

ticket: 7408
Remove unused texinfo sources

Now that the admin guide make rules are removed, quite a few of the
texinfo sources are not referenced from anywhere and can be safely
removed.

ticket: 7408
Allow null inputs to response item functions
Add responder support to get_as_key()

This follows the design laid out on the project page:
  http://k5wiki.kerberos.org/wiki/Projects/Password_response_item
Add responder support to preauth_encts/preauth_ec
Fix a couple of typos
Add an input ccache get_init_creds option

Add a krb5_get_init_creds_opt_set_in_ccache() function.  An input
ccache may hold configuration data which the client libraries can
use to influence their decisions.
Use hex escapes for non-printable parts of {str}/{lenstr}/{data}

When adding {str}, {lenstr}, or {data} to trace output, scan for
bytes which might be non-printable, and add them as hex-escaped
versions of themselves if any are found.
Add a -C flag to klist to also show config entries
Add "pa_types" configuration to ccaches

* When producing preauth data, keep track of the types of padata which
  the module that produced the data can handle.  Originally this was
  just the type of data we'd produced, but that caused problems for
  PKINIT.
* After obtaining credentials, store that list of preauth types as a
  "pa_types" configuration item in the out_ccache.
* Read a list of allowed preauth types from an in_ccache, if possible.
* If we have a list of allowed preauth types, skip any "real" modules
  which aren't in that list.
Test in_ccache and pa_types functionality

* Add a krb5int_build_conf_principals() function to allow our get/set
  code to directly prune out duplicate config entries.
* Verify that when we specify pa_types, they affect whether or not we
  will use a particular preauth mechanism.
* Verify that we correctly save the list of preauth mechanisms that are
  used in out_ccaches.
Add "pa_config_data" configuration to ccaches

* Read a "pa_config_data" item from an in_ccache, if provided, and add a
  callback which client preauth plugins can use to retrieve a string
  value that's keyed by a string.
* Add a callback which client preauth plugins can use to provide string
  key/value pairs to be stored in the ccache.
Use config storage for client identity selection

* Keep track of the names of client identities when we load them.
* Store the client identity we just used when we create or retry a
  client request.
* If we read a client identity from the configuration, treat it like the
  KDC does: pick the "this is it, there is no other" logic branch.
Use config storage for client OTP token selection

* Save the vendor name of the token we used to create the challenge.
* If we saved the name of a token vendor previously, prune out any
  tokeninfos which contain different vendor names.
Reset the prompt_types list after calling prompters

Reset the prompt_types list immediately after the prompter callback
returns, as is done everywhere else.
Sanity-check loading keys and certs from PEM files

Print a debug message if we're unable to locate the matching private key
for a certificate when we've just loaded both of them from PEM files.
Agility fix: don't try to free an uninitialized keyblock.
Make sure that pkinit_octetstring_hkdf() initializes NSS

Create an NSS context for use when performing KDF, so that the tests,
which call into the function directly, will work.
Handle anonymous-as-signed-data-with-no-signers

Update to generate and consume signed-data with no signer-info, which we
need for anonymous PKINIT.