Text field fixes

These are the two fix commits from Pull Request #1021, along with two other commits in response to comments on that request. Although they are orthogonal commits, they can't be automatically merged if applied independently so I'm just putting them all in one request. The first two commits didn't have any comments from @dcporter and the next two were requested by @dcporter so there shouldn't be any problem accepting them.

The last two commits are in response to:

> I recommend using SC.none() here instead of != null - if (!SC.none(autocomplete)) will catch undefined as well as null (in case the developer does something weird).

and:

> Also, I assume that the attribute itself is case-insensitive, I think this will read more smoothly if you use input.attr('autocomplete', ...);

Which were both problems with the original code, so fixing them now will make everything consistent when my feature pull requests are made.

Thanks!