add support for --html

* bootstrap.conf: We need the "execute" module.
* src/files.h, src/files.c (spec_html_file, html_flag): New.
* src/getargs.h, src/getargs.c (--html): New.
* src/print-xml.h, src/print-xml.c (print_html): New.
* src/main.c: Use them.
* tests/output.at, tests/report.at: Check --html.

src/main.c

@@ -188,12 +188,20 @@ main (int argc, char *argv[])
         }
 
       /* Output xml.  */
-      if (xml_flag)
+      if (html_flag || xml_flag)
         {
           timevar_push (tv_xml);
           print_xml ();
           timevar_pop (tv_xml);
         }
+
+      /* Output html.  */
+      if (html_flag)
+        {
+          timevar_push (tv_html);
+          print_html ();
+          timevar_pop (tv_html);
+        }
     }
 
   /* Stop if there were errors, to avoid trashing previous output