Changes -g so that byte runs are still calculated (while still not reading data). Adds -b to avoid outputting byte runs at all if other data access options are disabled. Either option should be used in concert with '-z' to avoid hashing data.
Output an error message if -g conflicts with other options requiring data access.
Merge pull request #155 from jonstewart/master

Allow fiwalk to output byte runs/extents to dfxml without reading file contents