This patch ensures that priority values passed as session arguments
are within the valid range of priorities. Without the clamping, a child
could specify a priority of a lower priority band than the one assigned
to the subsystem. Thanks to Johannes Schlatow for reporting this issue.
Fixes#1279
This patch changes the top-level directory layout as a preparatory
step for improving the tools for managing 3rd-party source codes.
The rationale is described in the issue referenced below.
Issue #1082