This helps working around missing C functions like strcasecmp that do
not exist everywhere (e.g. on Cygwin), and for which lib/ supplies a
replacement.  Unfortunately we do not have such build in our current
continuous integration suite, so we cannot easily detect files where
such config.h inclusion would be useful.  Therefore this patch simply
makes it mandatory to include config.h in *.cc files.  Including this
in public *.hh file is currently forbidden.

* spot/gen/automata.cc, spot/gen/formulas.cc,
spot/kripke/fairkripke.cc, spot/kripke/kripke.cc,
spot/ltsmin/ltsmin.cc, spot/misc/game.cc, spot/parseaut/fmterror.cc,
spot/parsetl/fmterror.cc, spot/parsetl/parsetl.yy,
spot/priv/bddalloc.cc, spot/priv/freelist.cc, spot/priv/satcommon.cc,
spot/priv/trim.cc, spot/priv/weight.cc, spot/ta/ta.cc,
spot/ta/taexplicit.cc, spot/ta/taproduct.cc, spot/ta/tgtaexplicit.cc,
spot/ta/tgtaproduct.cc, spot/taalgos/dot.cc,
spot/taalgos/emptinessta.cc, spot/taalgos/minimize.cc,
spot/taalgos/reachiter.cc, spot/taalgos/statessetbuilder.cc,
spot/taalgos/stats.cc, spot/taalgos/tgba2ta.cc, spot/tl/apcollect.cc,
spot/tl/contain.cc, spot/tl/declenv.cc, spot/tl/defaultenv.cc,
spot/tl/dot.cc, spot/tl/exclusive.cc, spot/tl/hierarchy.cc,
spot/tl/length.cc, spot/tl/ltlf.cc, spot/tl/mark.cc,
spot/tl/mutation.cc, spot/tl/nenoform.cc, spot/tl/print.cc,
spot/tl/randomltl.cc, spot/tl/relabel.cc, spot/tl/remove_x.cc,
spot/tl/simplify.cc, spot/tl/snf.cc, spot/tl/unabbrev.cc,
spot/twa/acc.cc, spot/twa/bdddict.cc, spot/twa/bddprint.cc,
spot/twa/formula2bdd.cc, spot/twa/taatgba.cc, spot/twa/twa.cc,
spot/twa/twagraph.cc, spot/twa/twaproduct.cc, spot/twaalgos/aiger.cc,
spot/twaalgos/alternation.cc, spot/twaalgos/are_isomorphic.cc,
spot/twaalgos/bfssteps.cc, spot/twaalgos/canonicalize.cc,
spot/twaalgos/cleanacc.cc, spot/twaalgos/cobuchi.cc,
spot/twaalgos/complement.cc, spot/twaalgos/complete.cc,
spot/twaalgos/compsusp.cc, spot/twaalgos/couvreurnew.cc,
spot/twaalgos/cycles.cc, spot/twaalgos/degen.cc,
spot/twaalgos/determinize.cc, spot/twaalgos/dot.cc,
spot/twaalgos/dtbasat.cc, spot/twaalgos/dtwasat.cc,
spot/twaalgos/dualize.cc, spot/twaalgos/emptiness.cc,
spot/twaalgos/gtec/ce.cc, spot/twaalgos/gtec/gtec.cc,
spot/twaalgos/gtec/sccstack.cc, spot/twaalgos/gtec/status.cc,
spot/twaalgos/gv04.cc, spot/twaalgos/hoa.cc,
spot/twaalgos/iscolored.cc, spot/twaalgos/isdet.cc,
spot/twaalgos/isunamb.cc, spot/twaalgos/isweakscc.cc,
spot/twaalgos/langmap.cc, spot/twaalgos/lbtt.cc,
spot/twaalgos/ltl2taa.cc, spot/twaalgos/ltl2tgba_fm.cc,
spot/twaalgos/magic.cc, spot/twaalgos/mask.cc,
spot/twaalgos/minimize.cc, spot/twaalgos/neverclaim.cc,
spot/twaalgos/parity.cc, spot/twaalgos/postproc.cc,
spot/twaalgos/powerset.cc, spot/twaalgos/product.cc,
spot/twaalgos/rabin2parity.cc, spot/twaalgos/randomgraph.cc,
spot/twaalgos/randomize.cc, spot/twaalgos/reachiter.cc,
spot/twaalgos/relabel.cc, spot/twaalgos/remfin.cc,
spot/twaalgos/remprop.cc, spot/twaalgos/sbacc.cc,
spot/twaalgos/sccfilter.cc, spot/twaalgos/sccinfo.cc,
spot/twaalgos/se05.cc, spot/twaalgos/sepsets.cc,
spot/twaalgos/simulation.cc, spot/twaalgos/split.cc,
spot/twaalgos/stats.cc, spot/twaalgos/strength.cc,
spot/twaalgos/stripacc.cc, spot/twaalgos/stutter.cc,
spot/twaalgos/sum.cc, spot/twaalgos/tau03.cc,
spot/twaalgos/tau03opt.cc, spot/twaalgos/totgba.cc,
spot/twaalgos/toweak.cc, spot/twaalgos/translate.cc,
spot/twaalgos/word.cc, tests/core/acc.cc, tests/core/bitvect.cc,
tests/core/checkpsl.cc, tests/core/checkta.cc, tests/core/consterm.cc,
tests/core/emptchk.cc, tests/core/equalsf.cc, tests/core/graph.cc,
tests/core/ikwiad.cc, tests/core/intvcmp2.cc, tests/core/intvcomp.cc,
tests/core/kind.cc, tests/core/kripkecat.cc, tests/core/length.cc,
tests/core/ltlrel.cc, tests/core/ngraph.cc, tests/core/parity.cc,
tests/core/randtgba.cc, tests/core/readltl.cc, tests/core/reduc.cc,
tests/core/safra.cc, tests/core/sccif.cc, tests/core/syntimpl.cc,
tests/core/taatgba.cc, tests/core/tostring.cc, tests/core/trival.cc,
tests/core/twagraph.cc, tests/ltsmin/modelcheck.cc,
spot/parseaut/scanaut.ll, spot/parsetl/scantl.ll: Include config.h.
* spot/gen/Makefile.am, spot/graph/Makefile.am,
spot/kripke/Makefile.am, spot/ltsmin/Makefile.am,
spot/parseaut/Makefile.am, spot/parsetl/Makefile.am,
spot/priv/Makefile.am, spot/ta/Makefile.am, spot/taalgos/Makefile.am,
spot/tl/Makefile.am, spot/twa/Makefile.am, spot/twaalgos/Makefile.am,
spot/twaalgos/gtec/Makefile.am, tests/Makefile.am: Add the -I lib/
flags.
* tests/sanity/includes.test: Catch missing config.h in *.cc, and
diagnose config.h in *.hh.
* tests/sanity/style.test: Better diagnostics.