Some Kidle refresh mode experiments...

Emulate (as best we can) the refresh behavior of the Kindle Touch reader
Try to use reagl on the PW2...

That doesn't seem to work as nicely as the stock reader... :/
Clear up some comments...
Another hugely important commit!
One more comment...
Keystrokes aren't that cheap.
Update koreader-base.

For the backend changes related to #704
Fix the battery checks.

I have *no* idea how that even seemed to work, but in fact didn't.
Also no idea where the hell is the battery status supposed to appear in
the menu, because it's currently not there.
Add a battery indicator to the menu.

Very quick'n dirty hack, doesn't seem to blow up horribly.
re: #679
Merge pull request #704 from NiLuJe/master

Some Kindle screen refresh experiments (bis)...