ltlcross: do not use f after it has been destroyed.

Reported by Joachim Klein.

* src/bin/ltlcross.cc: Here.
* NEWS, THANKS: Update.

NEWS

@@ -8,6 +8,7 @@ New in spot 1.1.2a (not releaased)
       the acceptance sets of an SCC but the first one were useless.
     - The script in bench/spin13/ would not work on MacOS X because
       of some non-portable command.
+    - A memory corruption in ltlcross.
 
 New in spot 1.1.2 (2013-06-09)
 

THANKS

@@ -10,6 +10,7 @@ Gerard J. Holzmann
 Heikki Tauriainen
 Jean-Michel Couvreur
 Jean-Michel Ilié
+Joachim Klein
 Kristin Y. Rozier
 Martin Dieguez Lodeiro
 Michael Weber

src/bin/ltlcross.cc

@@ -970,7 +970,6 @@ namespace
 	  nf->destroy();
 	}
 
-      f->destroy();
       cleanup();
       ++round;
 
@@ -999,6 +998,7 @@ namespace
 	}
 
       spot::ltl::atomic_prop_set* ap = spot::ltl::atomic_prop_collect(f);
+      f->destroy();
 
       for (unsigned p = 0; p < products; ++p)
 	{