infra: fix/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
light: fix logfile fetch from multiple peers
light: fix peer preferences, use connect-* links
marsadm: prevent only _new_ split brains
marsadm: fix leave-resource
marsadm: fix transitive closure for log_purge_res()
marsadm: fix warning
all: fix inconsistent terminology apply->replay

In most cases, "replay" was already used. So it is easier
to switch the rare "apply" wording to "replay" everywhere (hopefully).
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: update