strace signal handling regression

[Roland McGrath]

I put the change in.

> The INTERACTIVE flag meaning is unclear for me for me but this patch restores
> the original interruptible vs. uninterruptible behavior.  The PFLAG_SEEN flag
> should be IMO enough for the purposes the INTERACTIVE flag is currently in use.

I can't say I know what the rationale behind the flag was originally.
I only know what it does from reading the code.  The apparent effect is
that when using strace -o file command, it can just die immediately
without worrying about the state of partial syscall output.  I don't
really see why caring about displaying the final round of reports or
not depends on using -o.  Until fairly recent 2.6 kernels, it was
always necessary to do cleanup processing when using -p, to detach from
processes and be sure they would not be left stopped.


Thanks,
Roland