-browser: abstract downloadProgressCb calls with private functions initDownload or updateDownload
-browser: updateDownload with responseText.length at readyState == LOADING
dummyserver: add /bigslow and /utf8 resources
change API - "output" argument of "finished" option is now a "byte array" string
demo: load json2.js if needed
demo: always enable the button
demo: all text HTTP resources are now served with charset=UTF-8
test: add TODO items