It was never updating because we'd just seek the start of /proc/memstat
over and over, which didn't generate new contents. Instead, open the
file on every iteration.
We now use GLazyWidget for all the secondary tabs, which makes the
program start up way faster than before.
There's a noticeable delay when you click on the "PCI Devices" tab
for the first time, but that's definitely better than always eating
that delay before seeing a window at all. :^)
