add missing utf-8 header to many source files
* src/sanity/style.test: Test for the missing header.
* iface/ltsmin/check.test, src/kripketest/kripke.test,
src/kripketest/parse_print_test.cc, src/ltlparse/fmterror.cc,
src/ltltest/consterm.test, src/ltltest/kind.test,
src/ltltest/length.test, src/ltltest/ltlfilt.test,
src/ltltest/reduc.cc, src/ltltest/reduc.test,
src/ltltest/reduc0.test, src/ltltest/reducpsl.test,
src/ltltest/remove_x.test, src/ltltest/unabbrevwm.test,
src/ltltest/utf8.test, src/ltltest/uwrm.test, src/ltlvisit/dump.cc,
src/ltlvisit/remove_x.cc, src/misc/casts.hh, src/misc/fixpool.hh,
src/misc/hashfunc.hh, src/misc/ltstr.hh, src/sanity/readme.test,
src/taalgos/tgba2ta.cc, src/tgbaalgos/bfssteps.cc,
src/tgbaalgos/stats.cc, src/tgbatest/acc.test,
src/tgbatest/bitvect.test, src/tgbatest/complementation.test,
src/tgbatest/cycles.test, src/tgbatest/degendet.test,
src/tgbatest/dfs.test, src/tgbatest/dupexp.test,
src/tgbatest/emptchkr.test, src/tgbatest/intvcomp.test,
src/tgbatest/ltl2ta.test, src/tgbatest/ltl2ta2.test,
src/tgbatest/ltlprod.test, src/tgbatest/maskacc.test,
src/tgbatest/obligation.test, src/tgbatest/randpsl.test,
src/tgbatest/readsat.cc, src/tgbatest/readsat.test,
src/tgbatest/scc.test, src/tgbatest/sccsimpl.test,
src/tgbatest/taatgba.test, src/tgbatest/tgbaread.test,
src/tgbatest/tripprod.test, src/tgbatest/uniq.test,
src/tgbatest/wdba.test: Add it.
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