Fixed permission checking bug

[franga2000]

The globally_* variables were being overridden in the for f in forum loop, which screwed them up for the next iteration.

TL;DR: If your forums were ordered [public1, private, public2] it worked, public2 wasn't visible, because its permission check ran after the check for private. This fix simply renames the variables so nothing inside one loop iteration influences the next iteration.

For example:

• every user in a "members" group has global read permissions (globally_granted_group_perms = ["can_see_forum", "can_read_forum"])
• that group also has nongranted permissions for a specific forum, line an "admins only" forum (globally_nongranted_group_perms = ["can_see_forum", "can_read_forum"])
• on the "normal" forums, nothing is changed
• on the "admins only" forum, globally_granted_group_perms gets filtered to = []
• on the remaining "normal" forums, globally_granted_group_perms = [] is the starting point, so no permissions are returned

The test I added failed before the fix, now it passes.