MINOR: lua: Increase debug information

MINOR: lua: Increase debug information

When an unrecoverable error raises, the user receive poor information
for the trouble shooting. For example:

   [ALERT] 157/143755 (21212) : Lua function 'hello-world': runtime error: memory allocation error: block too big.

Unfortunately, the memory allocation error can be throwed by many
function, and we have no informatio to reach the original cause.
This patch add the list of function called from the entry point to
the function in error, like this:

   [ALERT] 157/143755 (21212) : Lua function 'hello-world': runtime error: memory allocation error: block too big from [C] method 'req_get_headers', bug35.lua:2 global 'ee', bug35.lua:6 global 'ff', bug35.lua:10 C function line 9.