cleanup gcc 4.8.2 warnings

clean up the following warnings reported by nightly dashboard:

* vtkDataArrayIteratorMacro: typedef X locally defined but not used.
disable the warning rather than remove the typedef which is
part of the templated API and needed by clients. This partially
reverts 5a92d0594a24a2 which removed the typedef.

* vtkFFMPEGWriter: missing initializer for member X

Change-Id: I343693fd482f3b76b44a7d48d6e0b5e538ec9311
Merge topic 'gcc-482-warnings' into master

c08211ba cleanup gcc 4.8.2 warnings