Better error messages for some polymorphic functions

New auxiliary functions/macros 'luaL_argexpected'/'luaL_typeerror'
ease the creation of error messages such as

  bad argument #2 to 'setmetatable' (nil or table expected, got boolean)

(The novelty being the "got boolean" part...)

1 files changed, 1 insertions, 1 deletions

diff --git a/lcorolib.c b/lcorolib.c
index 9038f9fb..34462b53 100644
--- a/lcorolib.c
+++ b/lcorolib.c
@@ -20,7 +20,7 @@
 
 static lua_State *getco (lua_State *L) {
   lua_State *co = lua_tothread(L, 1);
-  luaL_argcheck(L, co, 1, "thread expected");
+  luaL_argexpected(L, co, 1, "thread");
   return co;
 }