Fix autogrow behavior on long words, add variable width textarea support...

[Thinkscape]

Testing autogrow on long words (word-wrapping issue):

1. Create a textarea
2. Attach .autogrow() to it
3. Set cursor inside textarea, press and hold D
4. The textarea should now expand properly.

Testing variable width textarea

1. Create a textarea with width 50% (or auto inside a container)
2. Attach .autogrow() to it
3. Type in some text to make it grow
4. Optionally resize browser window
5. The textarea should now adjust automatically.

[akaihola]

Thanks @Thinkscape, this looks good!