PROBE-FILE on symlinks to pipes inside /proc on Linux.

PROBE-FILE on symlinks to pipes inside /proc on Linux.

PROBE-FILE now can access symlinks to pipes and sockets in
/proc/pid/fd/ on Linux.
query-file-system already has code for handling broken symlinks,
resolving the directory part, use it on files for which realpath(3)
fails, which includes pipes and socket links in /proc.

Reported by Eric Schulte.