* Move the Synced_interface from os -> base
* Align the naming of "synchronized" helpers to "Synced_*"
* Move Synced_range_allocator to core's private headers
* Remove the raw() and lock() members from Synced_allocator and
Synced_range_allocator, and re-use the Synced_interface for them
* Make core's Mapped_mem_allocator a friend class of Synced_range_allocator
to enable the needed "unsafe" access of its physical and virtual allocators
Fix#1697
This patch adds const qualifiers to the functions Allocator::consumed,
Allocator::overhead, Allocator::avail, and Range_allocator::valid_addr.
Fixes#1481
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
