Custom backends can allocate memory when reading objects and providing them to libgit2. However, if an error occurs in the custom backend after the memory has been allocated for the custom object but before it's returned to libgit2, the custom backend has no way to free that memory and it must be leaked. Provide a free function that corresponds to the alloc function so that custom backends have an opportunity to free memory before they return an error.
The `git_odb_backend_malloc` name is a system function that is provided for custom ODB backends and allows them to allocate memory for an ODB object in the read callback. This is important so that libgit2 can later free the memory used by an ODB object that was read from the custom backend. However, the name _suggests_ that it actually allocates a `git_odb_backend`. It does not; rename it to make it clear that it actually allocates backend _data_.
Update internal usage of `git_transfer_progress` to `git_indexer_progreses`.
`git_time_monotonic` was added so that non-native bindings like rugged could get high-resolution timing for benchmarking. However, this is outside the scope of libgit2 *and* rugged decided not to use this function in the first place. Google suggests that absolutely _nobody_ is using this function and we don't want to be in the benchmarking business. Remove the function.
`git_stream_register_tls` is now deprecated; mark it in an if guard with the deprecation. This should not be included in `deprecated.h` since it is an uncommonly used `sys` header file.
Since we now always build the library with cdecl calling conventions, our callbacks should be decorated as such so that users will not be able to provide callbacks defined with other calling conventions. The `GIT_CALLBACK` macro will inject the `__cdecl` attribute as appropriate.
git_object_t is the future; update the public API to use it. This will also ensure that we can build our tests which make use of the old API without modification (and without compiler warnings).
Accept an enum (`git_stream_t`) during custom stream registration that indicates whether the registration structure should be used for standard (non-TLS) streams or TLS streams.