Changed interface between traversal & mediator/union to pass a callback
function instead of a set of filenames to ignore. The function implemented
for Aufs replicates the previous ignore_files functionality, but the new
interface can examine more than just the filename (useful for union/overlay
filesystems that denote special files in other ways such as by using xattrs)
Changed name of IgnoreFileP() to IgnoreFilePredicate() for clarity.

Fixed some inadvertent tab-to-spaces whitespace issues.
Merge branch 'master' of https://github.com/cvmfs/cvmfs into cvmfs-master

Conflicts:
	cvmfs/sync_mediator.cc
	cvmfs/sync_mediator.h
adjust fs traversal unit test to ignore file name callback
minor modification to ignore filename callback, general spring cleaning of white spaces
authors list
Merge branch 'wtsi-hgi-feature/ignore-file-fn'