ls-files: honour per-directory ignore file from higher directories.

When git-ls-files -o --exclude-per-directory=.gitignore is run
from a subdirectory, it did not read from .gitignore from its
parent directory.  Reading from them makes output from these two
commands consistent:

    $ git ls-files -o --exclude-per-directory=.gitignore Documentation
    $ cd Documentation &&
      git ls-files -o --exclude-per-directory=.gitignore

Signed-off-by: Junio C Hamano <junkio@cox.net>

ls-files.c

@@ -474,8 +474,28 @@ static void show_files(void)
 		const char *path = ".", *base = "";
 		int baselen = prefix_len;
 
-		if (baselen)
+		if (baselen) {
 			path = base = prefix;
+			if (exclude_per_dir) {
+				char *p, *pp = xmalloc(baselen+1);
+				memcpy(pp, prefix, baselen+1);
+				p = pp;
+				while (1) {
+					char save = *p;
+					*p = 0;
+					push_exclude_per_directory(pp, p-pp);
+					*p++ = save;
+					if (!save)
+						break;
+					p = strchr(p, '/');
+					if (p)
+						p++;
+					else
+						p = pp + baselen;
+				}
+				free(pp);
+			}
+		}
 		read_directory(path, base, baselen);
 		qsort(dir, nr_dir, sizeof(struct nond_on_fs *), cmp_name);
 		if (show_others)