Allow install profiles to change the system requirements

imho there should be a way to change the constants defined for the system requirements
as 'DRUPAL_MINIMUM_PHP' or 'DRUPAL_MINIMUM_PHP_MEMORY_LIMIT'.
there could be some complex install profiles that requires "more power" from the system.
for example there's a Commerce Kickstart issue about this : #1763632: The install needs to check Kickstart requirements before starting.