fblualib/atomicvector/AtomicVector.h: avoid shadowing warnings
fblualib/atomicvector/AtomicVector.h: avoid shadowing warnings

Summary:
Fix warnings exposed by gcc-4.9.x's -Wshadow-compatible-local
(and/or the stricter -Wshadow-local) options.  Note that these
are both less onerous than -Wshadow.
I plan to enable one of them for all of fbcode, soon.

Rename inner (lambda parameter) "sz" to "siz".
Also rename inner (lambda parameter) "fd" to "readFd".

This avoids the following errors:

  fblualib/atomicvector/AtomicVector.h:347:71: error: declaration of 'sz' shadows a lambda capture [-Werror=shadow-compatible-local]
  fblualib/atomicvector/AtomicVector.h:346:60: error: shadowed declaration is here [-Werror=shadow-compatible-local]
  fblualib/atomicvector/AtomicVector.h:347:72: error: declaration of 'fd' shadows a lambda capture [-Werror=shadow-compatible-local]
  fblualib/atomicvector/AtomicVector.h:346:60: error: shadowed declaration is here [-Werror=shadow-compatible-local]

Reviewed By: andrewjcg, Gownta

Differential Revision: D4442692

fbshipit-source-id: a88e8b410667610392f6abd379cae37916b7c652

facebook/fblualib,facebook/fblualib