add ngettext support & optimize gettext handling

As I was adding ngettext support, I realized I could optimize the gettext
functions by memoizing the creation of the gettext object. Note that
the object creation is still deferred until a gettext function is called,
to avoid unnecessary startup penalties on code paths that do not need
gettext.

A side benefit is that separate stub functions are no longer needed to
handle the C language case.

IkiWiki.pm

@@ -20,7 +20,7 @@ use Exporter q{import};
 our @EXPORT = qw(hook debug error template htmlpage deptype
                  add_depends pagespec_match pagespec_match_list bestlink
 		 htmllink readfile writefile pagetype srcfile pagename
-		 displaytime will_render gettext urlto targetpage
+		 displaytime will_render gettext ngettext urlto targetpage
 		 add_underlay pagetitle titlepage linkpage newpagefile
 		 inject add_link
                  %config %links %pagestate %wikistate %renderedfiles
@@ -1820,27 +1820,38 @@ sub file_pruned ($;$) {
 sub define_gettext () {
 	# If translation is needed, redefine the gettext function to do it.
 	# Otherwise, it becomes a quick no-op.
-	no warnings 'redefine';
+	my $gettext_obj;
+	my $getobj;
 	if ((exists $ENV{LANG} && length $ENV{LANG}) ||
 	    (exists $ENV{LC_ALL} && length $ENV{LC_ALL}) ||
 	    (exists $ENV{LC_MESSAGES} && length $ENV{LC_MESSAGES})) {
-	    	*gettext=sub {
-			my $gettext_obj=eval q{
+	    	$getobj=sub {
+			$gettext_obj=eval q{
 				use Locale::gettext q{textdomain};
 				Locale::gettext->domain('ikiwiki')
 			};
-
-			if ($gettext_obj) {
-				$gettext_obj->get(shift);
-			}
-			else {
-				return shift;
-			}
 		};
 	}
-	else {
-		*gettext=sub { return shift };
-	}
+
+	no warnings 'redefine';
+	*gettext=sub {
+		$getobj->() if $getobj;
+		if ($gettext_obj) {
+			$gettext_obj->get(shift);
+		}
+		else {
+			return shift;
+		}
+	};
+  	*ngettext=sub {
+		$getobj->() if $getobj;
+		if ($gettext_obj) {
+			$gettext_obj->nget(@_);
+		}
+		else {
+			return ($_[2] == 1 ? $_[0] : $_[1])
+		}
+	};
 }
 
 sub gettext {
@@ -1848,6 +1859,11 @@ sub gettext {
 	gettext(@_);
 }
 
+sub ngettext {
+	define_gettext();
+	ngettext(@_);
+}
+
 sub yesno ($) {
 	my $val=shift;
 

doc/plugins/write.mdwn

@@ -911,6 +911,10 @@ time.
 
 This is the standard gettext function, although slightly optimised.
 
+### `ngettext`
+
+This is the standard ngettext function, although slightly optimised.
+
 ### `urlto($$;$)`
 
 Construct a relative url to the first parameter from the page named by the