Bug#924792: pidof: unsanitized user input makes pidof crash

[Jesse Smith]

I am certainly open to replacing the "format" flag (-f) with an
alternative field separator flag. It has a nice Unixy feel to it and
requires less code.

Personally, I think using -d (or --delimiter) might be the only change
I'd want to make to the patch KatolaZ provided. Partly because pidof
already has a lower-case "-s" flag and I want to avoid confusion, and
because tools like cut also use "-d".

If there are no objections, I'll upstream KatolaZ's patch and remove the
"-f" flag.

Jesse