use Perl

The last thing I'm working on is writing new tests for bleadperl. I noticed that there weren't tests for the command-line switches. I'm adding some. That's not the easiest thing to achieve, because this often involves launching a new perl interpreter, and portably.

Meanwhile, I fixed two bugs : the -s and -F switches didn't work when specified on the #! line. Well, for -F this is not an actual complete fix, merely a workaround, because I didn't reimplement a command-line parser for this sole purpose. So simple cases as

#!perl -F/xyz/

will now work, but don't expect

#!perl "-F/ /"

to work. In other words, whitespaces separate -F... from the next command-line argument.