assuming all the input R scripts are UTF8 encoded

ui.R, server.R, and global.R
make sure the HTML content is encoded in UTF8
make sure JSON messages are always encoded and decoded with UTF8

- per @jcheng5's suggestion, RJSONIO::fromJSON(encoding = 'UTF-8') actually works (no longer need my markUTF8 function)
- removed the global option 'shiny.transcode.json'
the cachedSource() function is not used anywhere, so perhaps we can remove it
UTF8 encoding for runApp(list(ui, server)) as well
Merge pull request #516 from yihui/bugfix/windows-encoding

Fixes #136: I18N support for Windows