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/system/libraries/Driver.php b/system/libraries/Driver.php
index 9a56013..1bc365c 100644
--- a/system/libraries/Driver.php
+++ b/system/libraries/Driver.php
@@ -290,7 +290,7 @@
 
 		$trace = debug_backtrace();
 		_exception_handler(E_ERROR, "No such method '{$method}'", $trace[1]['file'], $trace[1]['line']);
-		exit(EXIT_UNK_MEMBER);
+		exit(EXIT_UNKNOWN_METHOD);
 	}
 
 	// --------------------------------------------------------------------