Run scripts can use the new 'import_from_depot' function to incorporate
archive content from the depot into a scenario. The function must be
called after the 'create_boot_directory' function and takes any number
of pkg, src, or raw archives as arguments. An archive is specified as
depot-relative path of the form <user>/<type>/name. Run scripts may
call 'import_from_depot' repeatedly.
An argument can refer to a specific version of an archive or just the
version-less archive name. In the latter case, the current version (as
defined by a corresponding archive recipe in the source tree) is used.
If a 'src' archive is specified, the run tool integrates the content of
the corrsponding binary archive into the scenario. The binary archives
are selected according the spec values as defined for the build directory.
As of now, only x86_32 and x86_64 are supported by the 'depot_spec'
function.
Issue #2339
