Update 2012_12_06_225921_migration_cartalyst_sentry_install_users.php

Added indexes for activation_code and reset_password_code: so that methods findByActivationCode() and findByResetPasswordCode() are less time consuming.
Merge pull request #226 from semalead/patch-1

Update 2012_12_06_225921_migration_cartalyst_sentry_install_users.php