svn rev 3445: ScreenRepl.vim based on Jonathan Palardy's slime.vim
svn rev 3468: Handle errors from screen
svn rev 4026: Quote correctly to the shell
svn rev 4280: Newer screen -ls uses upcased "Attached"
svn rev 4280: Handle longer blocks of code with screen -X readreg, and handle Python newlines specially for the REPL
Call ScreenRepl_Vars() instead of Screen_Vars() which doesn't exist
Configure screen with msgwait 0, so it doesn't wait 5 seconds after pasting.