New functions 'lua_resetthread' and 'coroutine.kill'

New functions to reset/kill a thread/coroutine, mainly (only?) to
close any pending to-be-closed variable. ('lua_resetthread' also
allows a thread to be reused...)

lfunc.h

@@ -42,6 +42,17 @@
 #define MAXMISS		10
 
 
+/*
+** Special "status" for 'luaF_close'
+*/
+
+/* close upvalues without running their closing methods */
+#define NOCLOSINGMETH	(-1)
+
+/* close upvalues running all closing methods in protected mode */
+#define CLOSEPROTECT	(-2)
+
+
 LUAI_FUNC Proto *luaF_newproto (lua_State *L);
 LUAI_FUNC CClosure *luaF_newCclosure (lua_State *L, int nelems);
 LUAI_FUNC LClosure *luaF_newLclosure (lua_State *L, int nelems);