Modified show_error() to allow sending of HTTP server response codes.

Added set_status_header() to the Common functions to allow use when the Output class is unavailable.

Fixed a bug where the 400 status header sent with the 'disallowed URI characters' was not compatible with CGI environments.
diff --git a/user_guide/libraries/output.html b/user_guide/libraries/output.html
index 6d75fe7..ba6a0d3 100644
--- a/user_guide/libraries/output.html
+++ b/user_guide/libraries/output.html
@@ -100,7 +100,7 @@
 $this->output->set_header("Pragma: no-cache");	</code>
 
 
-<h2>$this->output->set_status_header();</h2>
+<h2>$this->output->set_status_header(<var>code</var>, '<var>text</var>');</h2>
 
 <p>Permits you to manually set a server status header.  Example:</p>