Don't include file type bits in tar archive's mode field.

The "file mode" bits in the tar file header is not supposed to include the
file type bits, e.g. S_IFREG or S_IFDIR. The file type is stored in a
separate field. This isn't a problem in practice, all tar programs ignore
the extra bits, but let's be tidy.

This came up in a discussion around bug #11949, reported by Hendrik Grewe,
although this doesn't fix the issue with tar --append. That turned out to be
a bug in GNU tar. Schilly's tartest program revealed this defect in the tar
created by pg_basebackup.

This problem goes as far as we we've had pg_basebackup, but since this
hasn't caused any problems in practice, let's be conservative and fix in
master only.

src/port/tar.c

@@ -77,8 +77,8 @@ tarCreateHeader(char *h, const char *filename, const char *linktarget,
 		h[flen + 1] = '\0';
 	}
 
-	/* Mode 8 */
-	sprintf(&h[100], "%07o ", (int) mode);
+	/* Mode 8 - this doesn't include the file type bits (S_IFMT)  */
+	sprintf(&h[100], "%07o ", (int) (mode & 07777));
 
 	/* User ID 8 */
 	sprintf(&h[108], "%07o ", (int) uid);