Fix #12545: Relationship graph output should use cmapx instead of cmap

The dot utility of Graphviz has -Tcmap and -Tcmapx output options that
correspond to HTML and XHTML output respectively. We should be using
"cmapx" to ensure that we're outputting a valid XHTML map element.

This commit also fixes incorrect permissions on graphviz_api.php
(removed execute bits).

core/relationship_graph_api.php

@@ -463,12 +463,16 @@ function relgraph_output_image( $p_graph ) {
 	$p_graph->output( 'png', true );
 }
 
-# Outputs an image map in HTML form (too bad dot didn't output XHTML...)
-# for the given relationship graph, previously generated by
-# relgraph_generate_graph_for_bug().
+/**
+ * Outputs an image map in XHTML format using the <map> element for the given
+ * relationship graph.
+ * @param Graph $p_graph Relationship graph object generated from relgraph_generate_graph_for_bug()
+ * @param string $p_name The XHTML name attribute to apply to the containing <map> element
+ * @return null
+ */
 function relgraph_output_map( $p_graph, $p_name ) {
 	echo '<map name="' . $p_name . '">' . "\n";
-	$p_graph->output( 'cmap' );
+	$p_graph->output( 'cmapx' );
 	echo '</map>' . "\n";
 }