This allows spawning a subprocess from a process using lots of memory without issue.
Otherwise the kernel will make sure we have in memeory+swap enough to accomodate 2*size of the parent process.

Made the non-implemented functions of Scheduler throw exceptions instead doing and returning nothing.

Fixed minor issues preventing the queueing of requests in SchedulerTest, DISABLED_archive_to_new_file

Added preliminary implementation of session's HandlerInterface which will communicate with the former. This class will
replace both TaskWatchDog and TapeServerReporter.
A new protocol buffer class (WatchdogMessage) was created to allow communication between the two.
Added the creation of the drive handler in the tape daemon.
Various minor fixes.

Fixed wrong shutdown status reporting in signal handler (it is always ready to shutdown).

Fixed process manager going to polling after timeout handler requested shutdown/kill/fork instead of handling the request.
Gathered the handlers for unit tests in a different file.