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...)

testes/main.lua

@@ -254,15 +254,15 @@ NoRun("error object is a table value", [[lua %s]], prog)
 
 
 -- chunk broken in many lines
-s = [=[ -- 
-function f ( x ) 
+s = [=[ --
+function f ( x )
   local a = [[
 xuxu
 ]]
   local b = "\
 xuxu\n"
   if x == 11 then return 1 + 12 , 2 + 20 end  --[[ test multiple returns ]]
-  return x + 1 
+  return x + 1
   --\\
 end
 return( f( 100 ) )
@@ -272,10 +272,10 @@ s = string.gsub(s, ' ', '\n\n')   -- change all spaces for newlines
 prepfile(s)
 RUN([[lua -e"_PROMPT='' _PROMPT2=''" -i < %s > %s]], prog, out)
 checkprogout("101\n13\t22\n\n")
-  
+
 prepfile[[#comment in 1st line without \n at the end]]
 RUN('lua %s', prog)
-  
+
 prepfile[[#test line number when file starts with comment line
 debug = require"debug"
 print(debug.getinfo(1).currentline)
@@ -306,6 +306,20 @@ NoRun("", "lua %s", prog)   -- no message
 prepfile("os.exit(false, true)")
 NoRun("", "lua %s", prog)   -- no message
 
+
+-- to-be-closed variables in main chunk
+prepfile[[
+  local *toclose x = function (err)
+    assert(err == 120)
+    print("Ok")
+  end
+  local *toclose e1 = function () error(120) end
+  os.exit(true, true)
+]]
+RUN('lua %s > %s', prog, out)
+checkprogout("Ok")
+
+
 -- remove temporary files
 assert(os.remove(prog))
 assert(os.remove(otherprog))