drupal_install_test creation fails when table already exists - fixed files included

To reproduce:

1) Start with a fresh install. Create a db user with ONLY Select, Update, Delete, and Insert permissions.
2) Proceed with install until you get to "Database configuration"
3) Proceed, and note the step eventually fails due to the db user failing to have CREATE TABLE permissions. Add only that permission to the db user.
4) Proceed, note the step fails again, due to not having DROP permissions. Add only that permission to the db user.
5) Proceed, note the step fails again, citing that the table drupal_install_test already exists. This is the specific problem I'm zero'ing in on.

5) happens due to drupal_install_test already existing due to it being created in a previous test run. However, if subsequent test runs fail, then the table is left in place, causing the error in 5). I've attached fixed files, note the added/commented lines:

/includes/mysql - lines 52 - 55
/includes/mysqli.inc - lines 57 - 60

Similar logic should be added to /includes/install/pgsql.inc.