As rados re-creates an object when trying to lock it, we tested for presence before locking.
This is racy as object could be deleted in the mean time.
Instead, we now lock blindly and delete the object if we find it having a zero-size.
As we own the lock, this is safe.

This problem led to issues in garbage colector, where agent gets polled while it could disappear.

This uncovered several failures to fetch again after relocking objects in unit tests (fixed as well).

Fixed calls to promise::get_future() after possible access form other thread. They are now guaranteed to happen before.
Added helgrind annotations for promise based synchronisation.
Added macros enabling helgrind annotations for shared_ptr.
Added suppression for shared_ptr used inside other standard lib object and not covered by the previous macros.
Added unit test for lower level .
Added suppressions for reported race conditions in Rados library.
Review heavily MemArchiveQueue and fixed missing commit in object store, leading to potentially orphaned objects.
Enabled formerly disabled test as it is now fast enough.

BackendVFS now throws the same exceptions as BackendRados.
The exceptions of the user provided update callback are now passed through.
A unit test was added.

The VFS implementation only launches the operation in the background (via std::async).
The Rados implementation uses the aio features of Rados. Lock and update are launched in the background via std::async.
Also now uses override for Backend virtual function.

Added url style conversion of checksums
Added support for checksums in mockNs
Fixed support for checksums in the scheduler
Re-instated several ASSERT_NO_THROW which were commented out during debugging.

Added tolerance to BackendRados::ScopedLock::release() when releasing a deleted object's lock.
Switched back to old style m_radosCtx.objects_begin() for compatibility with older releases of ceph.

Added a list method for the backends so we can clean up the rados store before running each unit test, which expects a fresh store.
Added a new command line tool to list the contents of the backends.

New URLs are rados://user@pool and file:///tmp/XXXXX. Otherwise, we fall back to interpreting
the URL as a bare path.

Created a richer protocol buffer RootEntry object and created a parital implementation to allow unit tests to run.

middletier, itself separated in interface, SQLite, objectstore and
shared tests.
Moved all utilities (exceptions, threading...) to a shared utility
directory.
Created a single, shared unit test from all the scattered ones.

License comment is no longer filtered out by doxygen when generating web pages of the individual source files.

The context handle concept is being dropped, with scoped lock objects in place.
The VFS backent store now compiles.