The intention of the previous change was to move krb5-config to .dev (it
gives the locations of headers), but it grabbed all of the user-facing
binaries too. This puts them back.
Allow switching out kerberos server implementation.
Sharing config is probably sensible, but implementation is different enough to
be worth splitting into two files. Not sure this is the correct way to split an
implementation, but it works for now.
Uses the switch from config.krb5 to select implementation.
