Updated exit codes as constant values

Re-allocated exit status codes according to three references, which follow:

BSD sysexits.h:http://www.gsp.com/cgi-bin/man.cgi?section=3&topic=sysexits
GNU recomendations:http://www.gnu.org/software/libc/manual/html_node/Exit-Status.html
Bash scripting:http://tldp.org/LDP/abs/html/exitcodes.html

The GNU recommendations stem from and expand upon the standard C/C++ library (stdlibc)
definitions, while also suggesting some best-practice conventions which happen to prevent
exit status code collisions with bash, and probably other shells.

The re-allocated codes are now mapped to constant values, set in *application/config/constants.php*,
and used throughout the CodeIgniter core.  They would additionally be used in *index.php*,
but the constants file hasn't been loaded at that point, so the integer values are used
instead, and a comment follows each such use with amplifying information on why that
particular value was selected.

Finally, the errors documentation has been updated accordingly.

Signed-off-by: Daniel Hunsaker <danhunsaker@gmail.com>

1 files changed, 1 insertions, 1 deletions

diff --git a/system/database/DB_driver.php b/system/database/DB_driver.php
index 6ae1d524d..18dbbc76e 100644
--- a/system/database/DB_driver.php
+++ b/system/database/DB_driver.php
@@ -1658,7 +1658,7 @@ abstract class CI_DB_driver {
 
 		$error =& load_class('Exceptions', 'core');
 		echo $error->show_error($heading, $message, 'error_db');
-		exit(5);
+		exit(EXIT_DATABASE);
 	}
 
 	// --------------------------------------------------------------------