Problem: Lua: can only execute on Vim command at a time. Not easy to get
the Vim version.
Solution: Make vim.command() accept multiple lines. Add vim.version().
(Yegappan Lakshmanan, closes#8716)
Problem: Testing the shell option is incomplete and spread out.
Solution: Move shell tests to one file and increase coverage. (Yegappan
Lakshmanan, closes#8464)