heads up (15.0 pkgbase): Kerberos package names

hello,

commit c7da9fb90b0b enabled WITH_MITKRB5 by default, which changed the
name of the Kerberos packages from FreeBSD-kerberos* to FreeBSD-krb5*.

i have just landed 4cb1baa7d85c to undo this change, so the packages are
now called FreeBSD-kerberos* again, no matter whether you build with MIT
Kerberos or Heimdal.

this also adds a new package called "FreeBSD-kerberos-kdc" containing
the MIT Kerberos KDC.  this package only exists if you use WITH_MITKRB5,
the location of the Heimdal kdc is unchanged.

there is one additional package called FreeBSD-kerberos-kdc-dev
(previously, FreeBSD-krb5-dev) which shouldn't exist and will be
deleted in a followup commit (see D51419).

manual action required:

* if you *don't* have the FreeBSD-krb5* packages installed (e.g., you
  haven't updated past c7da9fb90b0b yet) then you don't need to do
  anything, unless you want the MIT Kerberos kdc, in which case you
  should install FreeBSD-kerberos-kdc.

* if you do have the FreeBSD-krb5* packages installed, you should ensure
  that after you update past 4cb1baa7d85c, the old packages are removed:

	pkg remove -g 'FreeBSD-krb5*'

  you may then want to install the equivalent FreeBSD-kerberos packages
  instead.

* if you have build scripts that were broken by the original change to
  FreeBSD-krb5, and you fixed them at the time, you will need to "unfix"
  them to use the old names again.

* if you use Heimdal (i.e., you turned off WITH_MITKRB5) then nothing has
  changed for you and you do not need to do anything.