bug#11617: Don't use 'register'; these days it's not needed.

[Paul Eggert]

On 06/04/2012 06:06 AM, Stefan Monnier wrote:
> In my world, the keyword "register" is just another kind of whitespace.

It's a funny kind of whitespace that triggers compiler bugs
and makes code harder to read....  but I take your point and
won't remove 'register' all at once.