* src/bin/common_cout.cc, src/bin/common_cout.hh: New files.
* src/bin/Makefile.am: Add them.
* src/bin/ltl2tgba.cc, src/bin/ltlfilt.cc, src/bin/common_output.cc:
Report error when writing to std::cout failed. This is mainly
motivated by ltlfilt not being killed by SIGPIPE on lip6's OSX
buildfarm (SIGPIPE is probably ignored when the build is started), but
it could detect other errors such as a disk full.
