a bit more verbose ok() calls in event-ithreads.t
skip thread event tests under AUTOMATED_TESTING

this causes failure to build in Debian (http://bugs.debian.org/732324)

to trigger the crash, the test needs to be run in a loop, under
a very heavy system load. Here's a oneliner:

 ( export AUTOMATED_TESTING=1 ; C=0; while perl -Iblib/arch:blib/lib t/embed-80-event-ithreads.t; do C=$(( $C + 1 )); echo $C ; done )

I inspected some coredumps, and the segfault is at different place
every time, suggesting memory/stack corruption. Some of the backtraces
had traces from firebird shutdown sequence (presumably caused by the
embedded disconnect code) and some had tried to emit perl errors about
attempts to free unreferenced scalars and such.

My best guess for the core reason is the tricky concept of shutting
down FB engine (just look for 'shutdown' at tracker.firebirdsql.org),
which I guess sometimes doesn't play nicely with perl threads.

If my guess is right, it is not 100% safe to establish/close
connections via FirebirdEmbedded from perl threads.

Of course, the root cause may as well be in perl (though with the same
conclusion).

I added a TODO note to enable the tests again when FB3 comes out. If
it proves stable, we may enable the tests depending on FB version.