This patch improves the life-time management of socket descriptors and
addresses several corner cases exposed by the 'bomb' test.
The lookup and association of file descriptors with global IDs have been
turned into an atomic operation. Otherwise, multiple threads interacting
with the singleton 'ep_sd_registry' may override each other's
associations.
Closing the socket pair used for the reply channel has been implemented
via the RAII pattern to capture all corner cases, in particular
exceptions.
If blocking operations are interrupted by signals, we throw a
'Blocking_canceled' exception.
We preserve core's socket descriptor at 'PARENT_SOCKET_HANDLE' to avoid
a corner case where the parent capability is going to dup2'ed to the
same handle.
Support for 'Thread_base::join' within core to enable leaving Genode via
Control-C.
This patch simplifies the system call bindings. The common syscall
bindings in 'src/platform/' have been reduced to the syscalls needed by
non-core programs. The additional syscalls that are needed solely by
core have been moved to 'src/core/include/core_linux_syscalls.h'.
Furthermore, the resource path is not used outside of core anymore.
Hence, we could get rid of the rpath library. The resource-path code has
been moved to 'src/core/include/resource_path.h'. The IPC-related parts
of 'src/platform' have been moved to the IPC library. So there is now a
clean separation between low-level syscall bindings (in 'src/platform')
and higher-level code.
The code for the socket-descriptor registry is now located in the
'src/base/ipc/socket_descriptor_registry.h' header. The interface is
separated from 'ipc.cc' because core needs to access the registry from
outside the ipc library.
