Make the -F switch imply -a
[perl #116190] use the true and trusted fresh_perl_is()

instead of re-inventing it yet again
[perl #116190] -F and -a now imply -n
[perl #116190] feed an empty stdin to run_multiple_progs() programs

Two tests for -a were attempting to read stdin and blocking with the -a
implies -n change.
[perl #116190] -F implies -a, either implies -n

Previously -F without -a was a no-op, and -a without -n or -p was a
no-op, with this change, if you supply -F then both -a and -n are
implied (you can still use -p for its extra behaviour), and if you
supply -a then -n is implied.