swank protocol header use chars length rather than bytes && fix swank server address

hi, recently i'm using swank-js for remote debugging, and it's quite handy.

During using it, i found two problems:

* it doesn't support utf-8 properly. 
* swank-js-inject.js use the injected page address as swank server address

For ther first one, If my understanding is right, Swank protocol header use chars length rather than bytes.
For the second, i make swank-js-inject use it's script tag address.

This currently works well for me.