* lib/git-merge-changelog.c: Include idx.h.
(struct entry, entry_create, entry_hashcode)
(struct changelog_file, read_changelog_file)
(entries_mapping_get, entries_mapping_reverse_get)
(compute_mapping, struct edit, struct differences)
(compute_differences, find_paragraph_end)
(try_split_merged_entry, struct conflict, conflict_write, main):
Prefer idx_t to ptrdiff_t and size_t when the value is a
nonnegative index or size. Change a few for-loops so that
the index never goes negative.
* modules/git-merge-changelog (Depends-on): Add idx.