Added "emergency collection" to 'io.tmpfile' and 'os.tmpname'

These operations also can give errors for lack of resources, so they
also will try "emergency collections" in case of resource errors.
Because there are now two libraries with that kind of handling,
'resourcetryagain' was moved to the auxiliary library to be shared
by the libraries.

lauxlib.c

@@ -1,5 +1,5 @@
 /*
-** $Id: lauxlib.c,v 1.294 2018/02/27 18:47:32 roberto Exp roberto $
+** $Id: lauxlib.c $
 ** Auxiliary functions for building Lua libraries
 ** See Copyright Notice in lua.h
 */
@@ -290,6 +290,50 @@ LUALIB_API int luaL_execresult (lua_State *L, int stat) {
 /* }====================================================== */
 
 
+/*
+** {======================================================
+** 'luaL_resourcetryagain'
+** This function uses 'errno' to check whether the last error was
+** related to lack of resources (e.g., not enough memory or too many
+** open files).  If so, the function performs a full garbage collection
+** to try to release resources, and then it returns 1 to signal to
+** the caller that it is worth trying again the failed operation.
+** Otherwise, it returns 0.  Because error codes are not ANSI C, the
+** code must handle any combination of error codes that are defined.
+** =======================================================
+*/
+
+LUALIB_API int luaL_resourcetryagain (lua_State *L) {
+
+/* these are the resource-related errors in Linux */
+#if defined(EMFILE) || defined(ENFILE) || defined(ENOMEM)
+
+#if !defined(EMFILE)	/* too many open files in the process */
+#define EMFILE		-1	/* if not defined, use an impossible value */
+#endif
+
+#if !defined(ENFILE)	/* too many open files in the system */
+#define ENFILE		-1
+#endif
+
+#if !defined(ENOMEM)	/* not enough memory */
+#define ENOMEM		-1
+#endif
+
+  if (errno == EMFILE || errno == ENFILE || errno == ENOMEM) {
+    lua_gc(L, LUA_GCCOLLECT);  /* try to release resources with a full GC */
+    return 1;  /* signal to try again the creation */
+  }
+
+#endif
+
+  return 0;  /* else, asume errors are not due to lack of resources */
+
+}
+
+/* }====================================================== */
+
+
 /*
 ** {======================================================
 ** Userdata's metatable manipulation