BUG: Add portable access to Tiff field name

Macros were introduce to access the name in the TIFF field
structure. With libtiffv4 the TIFFFieldInfo data structure became
opaque and libtiff functions were required to access this
information. itkTIFFImageIO uses macros to portable access this for
compatibility with system libtiff libraries.

Change-Id: I863fe0ee5505741aebe73ddebea2034d64b72e95
Merge topic 'TIFFSystemLibraryCompatibility'

7cc65b1a BUG: Add portable access to Tiff field name