light: fix string memleak
infra: fix readlink() for very long paths
infra: fix removal of stale directories
light: fix potential race on deletions
infra: remove buggy d_{name,path}len

In rare cases, this could lead to buffer overflows.
Replace buggy concept from the prototype phase with more
robust (although slightly less performant) code.
marsadm: disallow intended primary switch when secondaries are syncing
infra: add flood protected syslogging
light: add per-resource emergency mode
light: add info symlinks
light: show connection info
copy: add timestamp of last advance
light: show new {fetch,sync} info
marsadm: path correction / systematic naming conventions
light: allow limiting the sync parallelism
marsadm: implement new 'view' command
zzz debug
doc (preliminary)