Bugfix for commit 79b8de103adc, the to_root() was too early.
Fix a an endless recursion if unlink() or rmdir() fails (fixes a segfault).
rmdir: to_root() needs to be called before the recursion.
Fix a missing to_user() in path_create()
Merged Bernd's bugfixes.
Renamed disable_initgroups to noinitgroups.
rename: copy-on-write was done too early.
rename: Use the return value of the whiteout creation.
rename: If rename() failed we need to remove the whiteout and cow-copied faile.
rename: We need cow for destdir 'to' as well.
rename: Hide (delete) files/directories in lower branches.
rmdir: Create a whiteout directory instead of a whiteout file.
readdir: Don't read dirs blacklisted by a whiteout.
Todo for unionfs_rename().
Set st_nlink for directories to one.
Move the hide_tag() function to general.c and rename it to whiteout_tag().
Add string_too_long() function to allow better string length.
Proper copy-on-write support for rmdir().
Just a comment for union_mkdir().
Improve string_too_long() by introducing the macro STR_TOO_LONG.