Permission check for results.txt should be made at start of the run

[thulle]

After churning through 36TB of data I'm met with:

Totally, 3 TiB can be reduced.
Now making results file results.txt
could not open file "results.txt"

While my user has permission to read and write all the checked files, I did not have permission to write in the topmost folder.. moving the check to the start of the run would probably save other idiots a few hours :D

[bordenc]

In keeping with the Unix Philosophy, perhaps rdfind should print to standard output by default. The output can either be piped to another program and/or a file. Obviously, leave the -outputname option to save to a file. I understand that accidentally printing GB of results.txt to standard output is unproductive, but at least someone would discover the mistake in their command when their console starts filling up rather than at the end of a multi-hour scan.