Fixes #56.

* src/bin/common_aoutput.cc, src/bin/common_aoutput.hh,
src/bin/dstar2tgba.cc: Implement it.
* src/bin/autfilt.cc, src/bin/ltl2tgba.cc, src/bin/ltldo.cc,
src/bin/randaut.cc: Fix main() to catch exceptions from the
constructor of the automaton printer as well.
* src/tgbatest/randaut.test: Add a test case.
* doc/org/oaut.org: Document it.