add more checks on input values

doc/man/man5/slapd.conf.5

@@ -1552,7 +1552,7 @@ The \fBscope\fP defaults to \fBsub\fP, the \fBfilter\fP defaults to
 \fBattrs\fP list defaults to \fB"*,+"\fP to return all user and operational
 attributes, and \fBattrsonly\fP is unset by default.
 The \fBsizelimit\fP and \fBtimelimit\fP only
-accept integers and both default to 0 (meaning unlimited).
+accept "unlimited" and positive integers, and both default to "unlimited".
 The LDAP Content Synchronization protocol has two operation types.
 In the
 .B refreshOnly