lalr1.cc: fix compiler warnings

Reported by Rob Conde.
http://lists.gnu.org/archive/html/bug-bison/2013-03/msg00003.html

* data/stack.hh (operator=, stack(const stack&)): Make this class
uncopyable, i.e., "undefine" these operators: make them private and
don't implement them.
(clear): New.
* data/lalr1.cc: Use it instead of an assignment.
(parser): Make this class uncopyable.

THANKS

@@ -103,6 +103,7 @@ Ralf Wildenhues           [email protected]
 Richard Stallman          [email protected]
 Rob Vermaas               [email protected]
 Robert Anisko             [email protected]
+Rob Conde                 [email protected]
 Satya Kiran Popuri        [email protected]
 Sebastian Setzer          [email protected]
 Sebastien Fricker         [email protected]