This patch changes the depot layout such that each archive is
represented as a directory that contains the versions of the archive as
subdirectories.
Issue #2610
The depot tool did not consistently distinct libraries from regular
targets when handling binary archives. The binary archive of a regular
target is located at <user>/<bin>/<arch>/<name> whereas a library is
located at <user>/<bin>/<arch>/<api>/<name>.
Fixes#2438
