bholtsclaw/pressflow-6-plus — comment on commit 044308d234db46c17f602145dcde69a428344773
File:  line 0
By bholtsclaw:

Sure, its for anything that bootstraps drupal outside of drupal, or even inside if its not a module or something else, eg my_script.php that does something like works right now, with the DRUPAL_ROOT changes it does not unless the DRUPAL_ROOT is defined before the include thus needing to change it in every other software that may use it, as well as multi places in drupal as you've seen with the original patch, this eliminates the need to change any external software so it will still work as it did before AND allows the DRUPAL_ROOT to be defined prior as your also doing.,

the only reason for the if(!defined) is because in your patch you are defining it before including bootstrap , otherwise just remove the other defines and leave this one to cover them all as in d7