gtk-demo: Ignore some lines in info

Ignore lines starting with # in the info comment at
the top of source files. This will be used to add
keywords for search in following commits.

demos/gtk-demo/main.c

@@ -581,6 +581,9 @@ load_file (const char *demoname,
               while (g_ascii_isspace (*(p + len - 1)))
                 len--;
 
+              if (*p == '#')
+                break;
+
               if (len > 0)
                 {
                   if (in_para)