Problem in nginx lua module.

call rex_pre.new in init_by_lua phase then call rex_pre.match in access_by_lua phase got following error messages:

```
550 2015/11/10 11:21:34 [error] 28259#0: *154 lua entry thread aborted: runtime error:###########/siglib.lua:31: error PCRE_ERROR_BADMAGIC
```

But when I try it in bash with luajit, everything is OK.  Is it a compatibility problem?
