Allow specifying runing user and chroot() enviroment

Allow the admin to switch the user the kdc is running under and
specify the chroot() directory to run in.

Please note you need a very special setup to get this working.

kdc/kdc_locl.h

@@ -67,6 +67,9 @@ extern const struct units _kdc_digestunits[];
 extern struct timeval _kdc_now;
 #define kdc_time (_kdc_now.tv_sec)
 
+extern char *runas_string;
+extern char *chroot_string;
+
 void
 loop(krb5_context context, krb5_kdc_configuration *config);