dir: select directories correctly

When matching a path against a list of patterns, the ones that require a directory match previously did not work when a filename is specified. This was fine when all pattern-matching was done within methods such as unpack_trees() that check a directory before recursing into the contained files. However, other commands will start matching individual files against pattern lists without that recursive approach. The last_matching_pattern_from_list() logic performs some checks on the filetype of a path within the index when the PATTERN_FLAG_MUSTBEDIR flag is set. This works great when setting SKIP_WORKTREE bits within unpack_trees(), but doesn't work well when passing an arbitrary path such as a file within a matching directory. We extract the logic around determining the file type, but attempt to avoid checking the filesystem if the parent directory already matches the sparse-checkout patterns. The new path_matches_dir_pattern() method includes a 'path_parent' parameter that is used to store the parent directory of 'pathname' between multiple pattern matching tests. This is loaded lazily, only on the first pattern it finds that has the PATTERN_FLAG_MUSTBEDIR flag. If we find that a path has a parent directory, we start by checking to see if that parent directory matches the pattern. If so, then we do not need to query the index for the type (which can be expensive). If we find that the parent does not match, then we still must check the type from the index for the given pathname. Note that this does not affect cone mode pattern matching, but instead the more general -- and slower -- full pattern set. Thus, this does not affect the sparse index. Helped-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com> Signed-off-by: Derrick Stolee <dstolee@microsoft.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>