Updated in accordance with feedback from @narfbg

- Removed commented lists of constants from the three reference conventions,
  replacing each with the URLs at which more information can be found.
- Renamed a few constants to more closely reflect CodeIgniter conventions.
- Modified a couple of lines which were in violation of the CI Style Guide.

Signed-off-by: Daniel Hunsaker <danhunsaker@gmail.com>
diff --git a/index.php b/index.php
index a52a021..c6314da 100755
--- a/index.php
+++ b/index.php
@@ -68,7 +68,7 @@
 	default:
 		header('HTTP/1.1 503 Service Unavailable.', TRUE, 503);
 		echo 'The application environment is not set correctly.';
-		exit(1); // EXIT_* constants not yet defined; 1 is EXIT_FAILURE, a generic error.
+		exit(1); // EXIT_* constants not yet defined; 1 is EXIT_ERROR, a generic error.
 }
 
 /*