H5Eset_auto for all threads

`H5Eset_auto()` sets the behaviour for the current thread. For h5py, it would be useful to have a similar function which affects either all threads, or the default for new threads. We want to suppress the HDF5 traceback by default, as we're turning it into a Python exception. At present, we work around this by calling `H5Eset_auto()` before every call of other HDF5 functions, just in case we're in a new thread.

For some amusing context, this was first requested 14 years ago :wink: : https://forum.hdfgroup.org/t/h5eset-auto-for-all-threads/1501