* configure.ac: Output src/ltlenv/Makefile.

* src/ltlenv/Makefile.am, src/ltlenv/defaultenv.cc,
src/ltlenv/defaultenv.hh, src/ltlenv/environment.hh: New files.
* src/ltlparse/public.hh (parse): Take an environment as third
argument.
* src/ltlparse/ltlparse.yy (ATOMIC_PROP, parse): Require the
atomic proposition via the environment.
* src/ltltest/readltl.cc (main): Adjust the call to parse().
* src/ltltest/Makefile.am (LDADD): Add ../ltlenv/libltlenv.a.

src/ltlenv/defaultenv.cc

@@ -0,0 +1,33 @@
+#include "defaultenv.hh"
+
+namespace spot
+{
+  namespace ltl
+  {
+
+    atomic_prop*
+    default_environment::require(const std::string& s)
+    {
+      return new atomic_prop(s);
+    }
+
+    const std::string&
+    default_environment::name()
+    {
+      static std::string name("default environment");
+      return name;
+    }
+
+    default_environment::default_environment()
+    {
+    }
+
+    default_environment& 
+    default_environment::instance()
+    {
+      static default_environment* singleton = new default_environment();
+      return *singleton;
+    }
+
+  }
+}