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.

 - Use regular expression to parse lines
 - More consistent error handling
 - More comprehensive error messages

Implement proper error propagation and handling on get_dirents RPC.
Error happening on the deamon are now embedded on the returned response
and the client throws an exception once he receives the response.