Merging in latest from upstream (HDFFV/hdf5:refs/heads/hdf5_1_12)
* commit '943129f61000899e394b75405723a3f110a21205':
Add note to release notes.
Change thread IDs to uint64_t from unsigned long, per Quincey's suggestion.
Add thread_id.c to the MANIFEST and the CMakeLists.txt per Allen's request.
Replace pthread_self_ulong() with H5TS_thread_id(). The POSIX Threads implementation ought to be portable to any system that has POSIX Threads. On Windows, I use the same API call as before.
Align contents of CMake and autotools testfile cleanup lists.
Avoid allocating a chunk index for datasets with 0-sized dimensions, until the dataset is extended.
