Merge pull request #1 from cvmfs/master

pull from upstream cvmfs
Added preliminary support for overlayfs.
Merge branch 'master' of https://github.com/wtsi-hgi/cvmfs into feature/overlayfs
Fixed a bug in cvmfs_listxattr that was causing it to return a null string in the middle of the list of
extended attributes for regular files.
Fixed a bug in cvmfs_listxattr that was causing it to return a null string in the middle of the list of
extended attributes for regular files.
Merge branch 'feature/overlayfs' of https://github.com/wtsi-hgi/cvmfs into feature/overlayfs
Removed 'TEST' from debug log for cvmfs_listxattr
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)
Merge branch 'feature/overlayfs' into feature/ignore-file-fn

Conflicts:
	cvmfs/sync_mediator.cc
	cvmfs/sync_mediator.h
Merge branch 'master' of https://github.com/wtsi-hgi/cvmfs

Conflicts:
	cvmfs/cvmfs_server