Check for failing 'stat' and skip this loop iteration

Check for failing 'stat' and skip this loop iteration
(since data in statbuf are invalid).

Check whether sysconf managed to find _SC_PAGESIZE.

Report at least debug warning about failing unlink
(logging scheme here seems to be a different then in lvm).

Duplicate terminal FDs and use similar code as is made in clvmd
and cleanup warns about missing open/close tests.
FIXME: Looks like we already have 3 instancies of the same code in lvm repo.