Disable autocmd on vimgrep call...

If you've set QuickFixCmdPost e.g. in vimrc:

  autocmd QuickFixCmdPost [^l]* nested cwindow

... the vimgrep result will be shown in a quickfix window and disable syntax
highlighting.

Since we're not particularly interested vimgrep's results (`echo $CLASSPATH` is
plenty), disable prefix with noautocmd. Alternatively, `:set
eventignore=QuickFixCmdPost` could be used here, the noautocmd was chosen for
the sake of brevity.