Merge branch 'jk/combine-diff-cleanup'

Code clean-up for code paths around combined diff. * jk/combine-diff-cleanup: tree-diff: make list tail-passing more explicit tree-diff: simplify emit_path() list management tree-diff: use the name "tail" to refer to list tail tree-diff: drop list-tail argument to diff_tree_paths() combine-diff: drop public declaration of combine_diff_path_size() tree-diff: inline path_appendnew() tree-diff: pass whole path string to path_appendnew() tree-diff: drop path_appendnew() alloc optimization run_diff_files(): de-mystify the size of combine_diff_path struct diff: add a comment about combine_diff_path.parent.path combine-diff: use pointer for parent paths tree-diff: clear parent array in path_appendnew() combine-diff: add combine_diff_path_new() run_diff_files(): delay allocation of combine_diff_path