Replace << "c" by << 'c', and check for it in style.sh
* src/sanity/style.test: Add a test.
* iface/dve2/dve2.cc, iface/dve2/dve2check.cc, src/bin/common_output.cc,
src/bin/dstar2tgba.cc, src/bin/ltl2tgba.cc, src/bin/ltlcross.cc,
src/dstarparse/dra2ba.cc, src/dstarparse/fmterror.cc,
src/dstarparse/nsa2tgba.cc, src/kripke/kripkeprint.cc,
src/kripkeparse/fmterror.cc, src/ltlast/atomic_prop.cc,
src/ltlast/bunop.cc, src/ltltest/ltlrel.cc, src/ltltest/reduc.cc,
src/ltltest/syntimpl.cc, src/ltlvisit/dotty.cc, src/ltlvisit/lbt.cc,
src/ltlvisit/randomltl.cc, src/ltlvisit/relabel.cc,
src/ltlvisit/simplify.cc, src/ltlvisit/tostring.cc, src/misc/bitvect.cc,
src/misc/optionmap.cc, src/misc/timer.cc, src/neverparse/fmterror.cc,
src/priv/freelist.cc, src/saba/sabacomplementtgba.cc,
src/sabaalgos/sabadotty.cc, src/taalgos/dotty.cc,
src/taalgos/minimize.cc, src/tgba/bdddict.cc, src/tgba/bddprint.cc,
src/tgba/futurecondcol.cc, src/tgba/taatgba.hh,
src/tgba/tgbakvcomplement.cc, src/tgba/tgbasafracomplement.cc,
src/tgbaalgos/compsusp.cc, src/tgbaalgos/cycles.cc,
src/tgbaalgos/dotty.cc, src/tgbaalgos/dtbasat.cc,
src/tgbaalgos/dtgbasat.cc, src/tgbaalgos/emptiness.cc,
src/tgbaalgos/gtec/gtec.cc, src/tgbaalgos/gv04.cc,
src/tgbaalgos/lbtt.cc, src/tgbaalgos/ltl2tgba_fm.cc,
src/tgbaalgos/minimize.cc, src/tgbaalgos/neverclaim.cc,
src/tgbaalgos/powerset.cc, src/tgbaalgos/replayrun.cc,
src/tgbaalgos/save.cc, src/tgbaalgos/scc.cc, src/tgbaalgos/sccfilter.cc,
src/tgbaalgos/weight.cc, src/tgbaalgos/word.cc,
src/tgbaparse/fmterror.cc, src/tgbatest/bitvect.cc,
src/tgbatest/complementation.cc, src/tgbatest/intvcmp2.cc,
src/tgbatest/intvcomp.cc, src/tgbatest/ltl2tgba.cc,
src/tgbatest/randtgba.cc: Replace << "c" by << 'c' when
appropriate.
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