Rewrite all std::map<const formula*, ...> as

Sgi::hash_map<const formula*, ...>.

* src/misc/hash.hh: New file.
* src/misc/Makefile.am (misc_HEADERS): Add it.
* src/ltlvisit/dotty.cc (dotty_visitor::map): Use a hash_map instead
of a map.
* src/tgba/bdddict.hh (bdd_dict::fv_map, bdd_dict::vf_map,
bdd_dict::ref_set, bdd_dict::var_map): Define as hash_map or
hash_set.
* src/tgbaalgos/ltl2tgba_fm.cc (translate_dict::fv_map,
translate_dict::vf_map): Likewise.
* src/tgba/tgbabddconcretefactory.hh
(tgba_bdd_concrete_factory::acc_map_): Likewise.
* src/tgba/tgbatba.hh, src/tgbaalgos/reachiter.hh: Include <map>.

src/misc/hash.hh

@@ -0,0 +1,40 @@
+#ifndef SPOT_MISC_HASH_HH
+#  define SPOT_MISC_HASH_HH
+
+// See the G++ FAQ for details about this.
+
+#  ifdef __GNUC__
+#  if __GNUC__ < 3
+#    include <hash_map.h>
+#    include <hash_set.h>
+    namespace Sgi { using ::hash_map; }; // inherit globals
+#  else
+#    include <ext/hash_map>
+#    include <ext/hash_set>
+#    if __GNUC_MINOR__ == 0
+      namespace Sgi = std;               // GCC 3.0
+#    else
+      namespace Sgi = ::__gnu_cxx;       // GCC 3.1 and later
+#    endif
+#  endif
+#  else      // ...  there are other compilers, right?
+#   include <hash_map>
+#   include <hash_set>
+    namespace Sgi = std;
+#  endif
+
+namespace spot
+{
+
+  /// A hash function for pointers.
+  template <class T>
+  struct ptr_hash
+  {
+    size_t operator()(const T* f) const
+    {
+      return reinterpret_cast<const char*>(f) - static_cast<const char*>(0);
+    }
+  };
+}
+
+#endif // SPOT_MISC_HASH_HH