Detect and handle symlinking of plugins in plugin_basename().

props rmccue, MikeSchinkel, jdgrimes.
see #16953.

Built from https://develop.svn.wordpress.org/trunk@27158


git-svn-id: http://core.svn.wordpress.org/trunk@27024 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/functions.php

@@ -1433,6 +1433,23 @@ function path_join( $base, $path ) {
 	return rtrim($base, '/') . '/' . ltrim($path, '/');
 }
 
+/**
+ * Normalize a filesystem path.
+ *
+ * Replaces backslashes with forward slashes for Windows systems,
+ * and ensures no duplicate slashes exist.
+ *
+ * @since 3.9.0
+ *
+ * @param string $path Path to normalize.
+ * @return string Normalized path.
+ */
+function wp_normalize_path( $path ) {
+	$path = str_replace( '\\', '/', $path );
+	$path = preg_replace( '|/+|','/', $path );
+	return $path;
+}
+
 /**
  * Determines a writable directory for temporary files.
  * Function's preference is the return value of <code>sys_get_temp_dir()</code>,