Util.pm: fix bug in escape_dn_value()

The original implementation replaced any leading & trailing whitespace
with '\20', the replacement for SPACE (U+0020).
This could lead to tabulators, newlines, ... being wrongly replaced by '\20'.

This commit fixes the issue.

lib/Net/LDAP/Util.pm

@@ -564,7 +564,7 @@ my @values = @_;
 
   map { $_ =~ s/([\\",=+<>#;])/\\$1/og;
         $_ =~ s/([\x00-\x1F])/"\\".unpack("H2",$1)/oge;
-        $_ =~ s/(^\s+|\s+$)/"\\20" x length($1)/oge; } @values;
+        $_ =~ s/(^ +| +$)/"\\20" x length($1)/oge; } @values;
 
   return(wantarray ? @values : $values[0]);
 }