Fix a bug where `pack-objects` would not respect multiple `--filter`
arguments when invoked directly.
* rs/multi-filter-args:
list-objects-filter: remove OPT_PARSE_LIST_OBJECTS_FILTER_INIT()
pack-objects: simplify --filter handling
pack-objects: fix handling of multiple --filter options
t5317: demonstrate failure to handle multiple --filter options
t5317: stop losing return codes of git ls-files