Merge branch 'jk/incore-lockfile-removal'

The long-standing rule that an in-core lockfile instance, once it is used, must not be freed, has been lifted and the lockfile and tempfile APIs have been updated to reduce the chance of programming errors. * jk/incore-lockfile-removal: stop leaking lock structs in some simple cases ref_lock: stop leaking lock_files lockfile: update lifetime requirements in documentation tempfile: auto-allocate tempfiles on heap tempfile: remove deactivated list entries tempfile: use list.h for linked list tempfile: release deactivated strbufs instead of resetting tempfile: robustify cleanup handler tempfile: factor out deactivation tempfile: factor out activation tempfile: replace die("BUG") with BUG() tempfile: handle NULL tempfile pointers gracefully tempfile: prefer is_tempfile_active to bare access lockfile: do not rollback lock on failed close tempfile: do not delete tempfile on failed close always check return value of close_tempfile verify_signed_buffer: prefer close_tempfile() to close() setup_temporary_shallow: move tempfile struct into function setup_temporary_shallow: avoid using inactive tempfile write_index_as_tree: cleanup tempfile on error