[ascii] When doing the preview or reading from an ascii file we calcualte the number of lines by readLine()'ing. This takes a lot of time for big files (>1GB). In FileInfoDialog we make use of wc linux utility, if available, which is much faster. This dirty hack makes sure we use wc also for the preview and when reading from the file. The solution is not nice, we need to revisit this maybe later again.