Detect fail conditions on std::cout in user's tools.
* 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.