We have two places where we lookup the inherited-fd list
by name and dup() the descriptor found. I propose to factor
out this piece in a single inherited_fd() call. When
we will want to support inheritance for sockets or any
other files we'll simply add the inherited_fd() call
there.

I'm also thinking about moving the call to inherited_fd
into generic level, but the open_path() routine doesn't
allow to do it in a simple manner.

Also we have not yet finished issue with files-vs-inodes
mapping. Keeping all the logic in one function should
make the solution simpler.
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>