Avoid excessive name pollution in test files

Test files are more polite regarding the use of globals when locals
would do, and when globals are necessary deleting them after use.

testes/tpack.lua

@@ -35,7 +35,7 @@ print("\talignment: " .. align)
 
 
 -- check errors in arguments
-function checkerror (msg, f, ...)
+local function checkerror (msg, f, ...)
   local status, err = pcall(f, ...)
   -- print(status, err, msg)
   assert(not status and string.find(err, msg))