ticket: 7800

Previously, if you passed a service name with a realm part to a
kadm5_init function, you would get a KRB5_PARSE_MALFORMED error
because the code would internally append its own '@realm' suffix
before parsing the name.  Fix this as follows:

Change gic_iter so instead of producing a full service name, it
produces a krb5_principal which is taken from the cred it acquires.
Pass the client and full service name around as principals, rather
than strings, and use the gss_nt_krb5_principal name type to import
them in setup_gss().  Don't append a realm to the input service name;
instead, pass the input service name directly to the gic functions
(which do not need a realm in the service name and will ignore the
realm if one is present).  For the INIT_CREDS case, parse the input
service name with KRB5_PRINCIPAL_PARSE_IGNORE_REALM and then set the
realm.

ticket: 7800

The "realm" variable in init_any is used only to fill in the realm of
the service principal in gic_iter().  The service principal realm
should always be the realm we looked up config parameters for, so we
can supply that realm to get_init_creds() unconditionally and
eliminate the case where we use the client principal realm.

Also get rid of an outdated comment and an #if 0 block we will never
need again, and use SNPRINTF_OVERFLOW to check the snprintf result.

Provide default values in pre.in for PROG_LIBPATH, PROG_RPATH,
SHLIB_DIRS, SHLIB_RDIRS, and STOBJLISTS so that they don't have to be
specified in the common case.  Rename KRB5_RUN_ENV and KRB5_RUN_VARS
to RUN_SETUP (already the most commonly used name) and RUN_VARS.  Make
sure to use DEFINES for local defines (not DEFS).  Remove some other
unnecessary makefile content.

Read realm parameters directly from the profile in the KDC's
init_realm(), getting rid of the intermediate krb5_realm_params
structure.  Then get rid of krb5_realm_params and
krb5_read_realm_params, since nothing else uses it.

Mostly this gets rid of the trailing space on line 2 after
bb76891f5386526bdf91bc790c614fc9296cb5fa.

kadm5_create_policy and kadm5_modify_policy had _internal variants in
libkadm5srv (but not libkadm5clnt) which only existed to protect the
policy_refcnt field from modification over the wire.  Now that
policy_refcnt is no longer used, we don't need the separation.

Bump the library soname since this is technically an ABI change.

Since there is no overlap between the clpreauth and kdcpreauth
interface declarations, there's no particular reason to combine them
into one header.  For backward compatibility and convenience, leave
behind a preauth_plugin.h which includes both.