bin/xbps-rindex/remove-obsoletes.c: always opendir() pwd

If repodir is given as a relative path, it will not work because it will
try to open the dir relative to itself because it already chdir()ed into
repodir. This fixes xbps-rindex -r when relative paths are specified.

fixes #519

bin/xbps-rindex/remove-obsoletes.c

@@ -134,7 +134,7 @@ remove_obsoletes(struct xbps_handle *xhp, const char *repodir)
 		rv = errno;
 		goto out;
 	}
-	if ((dirp = opendir(repodir)) == NULL) {
+	if ((dirp = opendir(".")) == NULL) {
 		fprintf(stderr, "xbps-rindex: failed to open %s: %s\n",
 		    repodir, strerror(errno));
 		rv = errno;