ecurity improvement: jAuth::logout() can destroy the session if session_destroy=on in the configuration

Did also refactoring on the code about persistant cookie
Fixed jAuth: the new hash method couldn't be used by app that don't use the jauth module
Merge branch 'jelix-1.2.x' into jelix-1.3.x

Conflicts:
	build/manifests/jelix-lib.mn
Merge branch 'jelix-1.3.x' into jelix-1.4.x

Conflicts:
	lib/jelix/auth/jAuth.class.php
forgot to remove the password.php file from the manifest for jauth module
Merge branch 'jelix-1.2.x' into jelix-1.3.x
Merge branch 'jelix-1.3.x' into jelix-1.4.x
Fixed issue: jPref::get() return false for empty string instead of an empty string
jpref_admin module: fixed right needed to show the preferences menu item