GCC warns about uninitialized local variables in cases where no
initialization is needed, in particular in the overloads of the
'Capability::call()' function. Prior this patch, we dealt with those
warnings by using an (unreliable) GCC pragma or by disabling the
particular warning altogether (which is a bad idea). This patch removes
the superfluous warnings by telling the compiler that the variable in
question is volatile.
The new 'chroot' tool at 'os/src/app/chroot' allows for executing
subsystems within chroot jails on Linux. For using the tool, please
refer to the test case 'os/run/chroot.run'. Fixes#37
