Properly terminate "nimrod i" on end of file.

Nimrod in interactive mode got stuck in an infinite loop when
encountering EOF (Ctrl-D), unless GNU Readline was being used. This
change mimics the GNU Readline behavior in rdstdin.nim and calls quit(0)
when encountering EOF while reading from stdin in interactive mode.
Merge pull request #1242 from rbehrends/interactive-eof-fix

Properly terminate "nimrod i" on end of file.