fix 'vim' alias on 'vi'-only system
    
    Despite the fact that user installed 'vim-enhanced' package, the alias
    didn't stop notifying user that 'vim' is not installed till the shell
    was restarted.
    
    Newly, if /usr/bin/vim suddenly appears (vim-enhanced is freshly
    installed) the alias is mostly no-op and vim is used directly.
    
    On top of ^, if user touches the ~/.i-know-vim-is-vi file, 'vi' is
    silently started instead of 'vim' without the warning.
    
    Resolves: rhbz#1907800