avoid forcing syslog setting

This avoids forcing the setting to 0 if it was not set at all.

IkiWiki/Setup.pm

@@ -79,7 +79,7 @@ sub getsetup () { #{{{
         # disable logging to syslog while dumping, broken plugins may
 	# whine when loaded
 	my $syslog=$config{syslog};
-        $config{syslog}=0;
+        $config{syslog}=undef;
 
 	# Load all plugins, so that all setup options are available.
 	my @plugins=grep { $_ ne $config{rcs} } sort(IkiWiki::listplugins());

IkiWiki/Setup/Standard.pm

@@ -86,7 +86,7 @@ sub gendump ($) { #{{{
 	my @ret;
 	
 	# disable logging to syslog while dumping
-	$config{syslog}=0;
+	$config{syslog}=undef;
 
 	push @ret, dumpvalues(\%setup, IkiWiki::getsetup());
 	foreach my $pair (IkiWiki::Setup::getsetup()) {