Define log levels in docs and change default to 0-3.

We define the meaning of the various log levels in the man page
for krb5_openlog(3).  If logging configured and levels are not
specified, we change the default levels to 0-3 which should exclude
debugging messages which are generally only desired in exceptional
circumstances.

We also go through the KDC and adjust the levels to be appropriate.

lib/krb5/krb5_openlog.3

@@ -203,9 +203,29 @@ parameter to
 .Fn krb5_log
 is within this range (inclusive) the message gets logged to this
 destination, otherwise not. Either of the min and max valued may be
-omitted, in this case min is assumed to be zero, and max is assumed to be
-infinity.  If you don't include a dash, both min and max gets set to the
-specified value. If no range is specified, all messages gets logged.
+omitted, in this case min is assumed to be 0, and max is assumed to
+be 3.
+If you don't include a dash, both min and max get set to the
+specified value.
+.Ss Levels
+Each log message has a level as follows:
+.Bl -tag -width "xxx" -offset indent
+.It 0
+Critical conditions.
+This is a condition that should be corrected immediately, such as a
+corrupted Kerberos database.
+.It 1
+Errors.
+These are errors that occur in the normal processing of requests.
+.It 2
+Warning messages.
+On the KDC, this includes malformed requests and requests that
+are out of policy.
+.It 3
+Informational messages.
+.It 4-9
+Debugging messages with increasing obscurity as the level rises.
+.El
 .Sh EXAMPLES
 .Bd -literal -offset indent
 [logging]

lib/krb5/log.c

@@ -268,7 +268,7 @@ KRB5_LIB_FUNCTION krb5_error_code KRB5_LIB_CALL
 krb5_addlog_dest(krb5_context context, krb5_log_facility *f, const char *orig)
 {
     krb5_error_code ret = 0;
-    int min = 0, max = -1, n;
+    int min = 0, max = 3, n;
     char c;
     const char *p = orig;
 #ifdef _WIN32
@@ -285,6 +285,8 @@ krb5_addlog_dest(krb5_context context, krb5_log_facility *f, const char *orig)
 		max = min;
 	    }
 	}
+	if (c == '-')
+	    max = -1;
     }
     if(n){
 #ifdef _WIN32