Add a sanity check for installed private headers.
If an installed header has an associated *.cc file (in the source tree), but does not declare any SPOT_API symbol, something is fishy. Either that header should not be installed, or it is missing the SPOT_API markers. * src/sanity/private.test: New test. * src/sanity/Makefile.am: Call it. * src/ltlast/Makefile.am: Do not install formula_tree.hh. * src/ltlvisit/Makefile.am: Do not install mark.hh. * src/tgbaalgos/Makefile.am: Do not intall weight.hh.