Add section on updating from single-DES

There are, unfortunately, still some single-DES deployments out
there.  Try to help them along by documenting a procedure for
migrating to stronger crypto.

The texinfo install guide had a section on "upgrading", but it was
not really suitable for direct import into a RST document.  For one,
it gave a high profile to the on-disk incompatibilities in upgrades
to 1.1 and 1.2.  It also was driven at upgrading *to* triple-des (or RC4),
which are something of a dead-end.  This new text attempts to be more
general and applicable to today's environment.
Disconnect texinfo install guide from the build

Its content has been migrated to or superseded by the RST documentation,
split amongst krb_build and various sections of krb_admins.

A few portions of the texinfo document are simply no longer relevant
and do not need to be migrated.  In particular:
It's 2012; we don't need to specify that we require a C89 compiler.
It's 2012; it will be easy to get enough disk to build krb5.
The KADM5 tests are part of 'make check' and don't need separate documentation.
Shared library support is not limited to "a few operating systems".
We do not need to document incompatibilities with ancient/dead OSes.
kadmind4 and v5passwdd are no longer relevant.

ticket: 7408
Remove make glue for texinfo install guide

Towards removing the texinfo docs entirely.

ticket: 7408
Remove unused texinfo sources

Now that the install guide Make rules are removed, nothing references
build.texinfo or install.texinfo any more (other than the tgz target).

ticket: 7408
Document TXT records for realm lookup

Even though they are subject to vulnerabilities via DNS spoofing
and we accordingly don't recommend their use, we do have the code
to use them.  Just as we document dns_lookup_realm in krb5.conf(5),
document them here.

ticket: 7407
Wordsmith SRV records for KDCs

Tweak the wording a bit to be more clear and avoid using multiple
words deriving from the stem "use" in close succession.
Add a bit more about the getdate timespec

While here, change the name to "Hybrid time".  The routine involved
is get_date(), but that is not a good name to expose to users, as
it does a poor job conveying what the routine does.  In the context
of "time duration" and "absolute time", the "hybrid time" which can
represent either is at least a slight improvement in the name.

Whoever added "fortnight" must have had a sense of humor, as that's
not likely to see much use in setting principal expiration times, but
giving a better sense that some "natural-language" time specifications
are allowed is worthwhile.

The old texinfo document had a full list of accepted time zones in
an appendix, but I do not think that is necessary; we accept most
time zones, and give an error if we encounter a time zone (or other
specification) that we do not understand.  As such, "try it and see
if it fails" is probably better than an exhaustive list which may
grow stale.

ticket: 7407
Wordsmith in kadm5_acl.rst

Grammar fixup and avoid jargon.
kadm5.acl line order is important

Make it a special note in the documentation to help it stand out.
Make the kadm5.acl example sane

It is an eggregious security violation to give all admin principals
admin rights and then give all null instances permission to change
the password of the associated admin instance.

While here, don't assume that admin and root are the only non-null
instances, and correct the formatting of an entry with restrictions.
Correct kadm5.acl synopsis

The target principal and restrictions arguments are not orthogonal;
a target principal argument must be given in order for a restriction
list to be supplied.
Normalize format of kadmin option descriptions

Start with a capital letter and end with a full sentence, making
the description a sentence (or at least close to one).
Renormalize section tree for database section

This is a little awkward because a lot of the content is included
piecemeal from the kadmin man page, so we have to introduce a new
level of section ordering (i.e., a new character used to mark
a section) in order to get the included content to line up with the
right parts of the content we have in the main file.

Apparently this is not too hard because reST does not have a fixed
hierarchy of the valid section title adornment characters; the
order is instead implied by the order in which they appear in the
document.

If we skip a section header character in the sequence, every heading
below that is lost (not rendered).  As such, be sure to uniformly
renormalize everything, at least in this file.
Move cross-realm info to the cross-realm section

It's really not appropriate for the "examples" subsection of
"Adding, modifying and deleting principals".

While here, update the enctype recommendation for cross-realm principals
to something that does not include weak crypto.
Remove pronoun referent ambiguity

The policy must be unused, not the delete_policy command.
Wordsmith kdb5_util stash -f

The keyfile worth overriding is the one in kdc.conf; though this
would override kdb5_util's -sf argument, there is no reason to
pass both flags to the same invocation.
In any case, the "at startup" language is not really correct.
Update kdb5_util example output

This text has not caught up with changes to the utility itself.
As a side effect, our output text box is narrower and does not have
to scroll on as many browser windows.
Fix copy/paste errors in dbadmin

We should include the stashsrvpw content in that section, not
the list content.  Likewise, the list_policy content instead
of the destroy_policy content.
Fix ordered list style

Sphynx outputs class information that corresponds to its generated
basic.css, which we do not include.  This results in all lists,
even nested lists, using arabic numerals.
Import the class properties into kerb.css for now.
Improve the ktadd and ktremove synopses

Mention the options on the synopsis line, and do not imply that
the principal argument(s) for ktadd are optional.
reST line blocks are needed to keep the two forms of ktadd on
separate lines.