Some serious issues with the new -O option

[Stefano Lattarini]

I'm sorry to say that the new -O option can interact *badly*
with Automake-generated parallel testsuites (at least when they
are being run "interactively", that is, with the output of make
connected to a tty).

Let me elaborate a little (if you still have doubts or objections
after reading the considerations below, please do not hesitate to
ask for clarifications).

For long-running testsuite with lots of tests, the use of the '-O'
option prevents the results from the tests already run to be displayed
on the screen until the *whole* testsuite has run.  IMO, this destroys
feedback and readability of the output.  Try building GNU coreutils and
running its testsuite with "make -j2 -O" on a slowish system to see how
this can be annoying in practice.

Moreover, since the output of the recipes is no longer connected to
a terminal, automatic colorization of output no longer work: no more
good results in green and failures in red (unless the user forces
them by exporting AM_COLOR_TESTS to "always").

In defense of the '-O' option, I must say that I see how such an option
can be actually useful to produce more readable logs when the output is
being redirected to a file (so that one doesn't care about real-time
feedback on the console); but for most "interactive" usages, I believe
its downsides definitely overweight its advantages.

So please don't ever make that option the default; if you really really
want to, at least put in place some smart checks that only enable '-O'
when the output is *not* a tty, so that we can have the best of both
worlds (useful feedback for interactive runs, more readable logs for
batch runs).

Thanks,
  Stefano