Inserted missing newline
Merge branch 'master' of https://github.com/wtsi-hgi/cvmfs
Added warnings to swissknife sync for overlayfs when hardlink groups are
partially but not completely modified in a transaction. Prints a warning
with some suggested commands to correct the issue manually and then
aborts.

Also changed cvmfs_server so that if swissknife sync aborts, it remounts
the union mount RW so that the user can edit it.