* src/bin/common_conv.cc, src/bin/common_conv.hh: New files.
* src/bin/Makefile.am: Add them.
* src/bin/autfilt.cc, src/bin/ltlcross.cc, src/bin/ltlfilt.cc,
src/bin/ltlgrind.cc, src/bin/randaut.cc, src/bin/randltl.cc: Use them.