Don't rely on a separate upgrade action. Any request except for login
and unlock will trigger an upgrade, if you're an admin. Once the upgrade
is complete, the module will rename itself such that it will no longer
load.
Recent GNU/Linux systems use ext3 or ext4 file systems. These use HTree
to index files. Wikipedia says: "HTree indexing improved the scalability
of Linux ext2 based filesystems from a practical limit of a few thousand
files, into the range of tens of millions of files per directory. [...]
HTree indexes are available in ext3 when the dir_index feature is
enabled. [...] HTree indexes are turned on by default in ext4."
Thus, instead of working on balanced-page-directories.pl, we decided to
get rid of these sub-directories altogether.
Unfortunately, this is backwards incompatible. Users wanting to upgrade
will need to install the upgrade.pl extension in order to upgrade the
file database.
