Allow symlinks to be passed to the read and write file system utilities.
Disallow writes to symlinks with offsets in file system servers, this is
to ensure that writing the target of a symlink is an atomic operation.
Fixes#1604
This patch changes the top-level directory layout as a preparatory
step for improving the tools for managing 3rd-party source codes.
The rationale is described in the issue referenced below.
Issue #1082
