Workaround for USE_CONCURRENT_MAP seg fault on 32 bit systems with gcc 4.2.

Very few people are on 32 bit systems, let alone using a gcc so old, so
don't sweat the lower perf of turning USE_CONCURRENT_MAP off in that
case.  It's not even worth trying to track down exactly what's wrong.

Also note that all we know is that it core dumps with gcc 4.2, and is
fine with gcc 4.6 and 4.8. It's possible that we'll need to adjust the
test to also exclude other old gcc's, but we'll cross that bridge when
we get to it.
Tighten up error propagation through IC, IB, and oiiotool.

Now we get nice helpful error messages if any of the input images are
corrupt or incomplete.
More tightening up of error reporting for oiiotool.

Found all places that haphazardly wrote error messages or warnings to
cerr or cout, and replaced them with legit error() or warning() calls
so that they all behave the same way including proper exit of oiiotool
with the right return code.