ext2: fix a comically trivial memory leak when adding entries to ext2 directories.

As a useful side-effect, this also means newly-created directories are not created corrupt.
ext2: Ext2Directory::addEntry now increases inode refcount correctly.
ext2: '.' should be before '..' in ext2 directory layout (makes fsck happy)
ext2: update Ext2Node's internal idea of node size in Ext2Node::fileAttributeChanged

This helps fix directory i_size values.