Uncomment & correct capture-in-capture test
Uncomment & correct capture-in-capture test

In LPeg's test.lua these lines are

```lua
   assert(m.C(n):match(x) == x)
   assert(m.C(m.C(n)):match(x) == x)
```

suggesting that C(p) and C(C(p)) should both produce a single value. Actually
the second call is returning two values - the documentation for `lpeg.C(patt)`
says "If patt has other captures, their values are returned after this one".
[Section 5.1](http://www.lua.org/pil/5.1.html) of Programming in Lua documents
that Lua ignores additional return values from a function call, when the
call is inside an expression.

moreati/ppeg,moreati/ppeg