Fixes an issue where client applications such as ssh might attempt to
close all open fds, therefore also closing the fds used by the internal
components of the library such as Mercury.

lseek was triggering a number overflow by converting long to integer on
its return value

Added specific lseek test

Write errors happenig on deamons are now reported back to clients.
"No space left on device" error is now properly propagated to clients.