This patch introduces support for stacked file systems alongside new
glue for accessing file-system implementations provided via Genode's
new file-system-session interface.
Using stacked file systems, an arbitrary number of file systems (such
as tar archives or file systems implemented as separate Genode
components) can be composed to form one merged virtual file system.
An example is given via the 'ports/run/noux_bash.run' script. This run
script creates a virtual file system out of multiple tar archives each
containing the content of a particular GNU package. In addition, one
'ram_fs' is mounted, which enables Noux to perform write operations.
This way, the shell output can be redirected to a file, or files can
be saved in VIM.
Fixes#103.
