_s: simplifying functions.php by making some of the stuff happening there modular with functions being called in templates showing up in template-tags.php, little extras that won't produce a visible error if they're missing in tweaks, and wpcom stuff in wpcom

inc/tweaks.php

@@ -0,0 +1,52 @@
+<?php
+/**
+ * Custom functions that act independently of the theme templates
+ *
+ * Eventually, some of the functionality here could be replaced by core features
+ *
+ * @package _s
+ * @since _s 1.0
+ */
+
+/**
+ * Get our wp_nav_menu() fallback, wp_page_menu(), to show a home link.
+ *
+ * @since _s 1.0
+ */
+function _s_page_menu_args( $args ) {
+	$args['show_home'] = true;
+	return $args;
+}
+add_filter( 'wp_page_menu_args', '_s_page_menu_args' );
+
+/**
+ * Adds custom classes to the array of body classes.
+ *
+ * @since _s 1.0
+ */
+function _s_body_classes( $classes ) {
+	// Adds a class of single-author to blogs with only 1 published author
+	if ( is_multi_author() ) {
+		$classes[] = 'group-blog';
+	}
+
+	return $classes;
+}
+add_filter( 'body_class', '_s_body_classes' );
+
+/**
+ * Filter in a link to a content ID attribute for the next/previous image links on image attachment pages
+ *
+ * @since _s 1.0
+ */
+function _s_enhanced_image_navigation( $url, $id ) {
+	if ( ! is_attachment() && ! wp_attachment_is_image( $id ) )
+		return $url;
+
+	$image = get_post( $id );
+	if ( ! empty( $image->post_parent ) && $image->post_parent != $id )
+		$url .= '#main';
+
+	return $url;
+}
+add_filter( 'attachment_link', '_s_enhanced_image_navigation', 10, 2 );