New API to get open identifers across entire library

[mattjala]

Is your feature request related to a problem? Please describe. H5F_get_obj_ids and H5F_get_obj_count consider transient datatypes to be objects only when using the H5F_OBJ_ALL flag. This makes them useful for retrieving and closing all open identifiers, but is inconsistent with library semantics.

Describe the solution you'd like H5F_get_obj_ids and H5F_get_obj_count should only operate on objects that exist on files. A new API should be added to provide the "get all ids that need to be closed" functionality - either a new flag to these functions, or a new API call. Either way, this would be a breaking API change, so it won't go in until the next major release (1.15).

The work for this change is on feature/h5f_get_obj_rework. Currently, it changes the existing functions to not count transient datatypes in any case, but doesn't include any way to get all open ids.