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.