sequencer.c: fix and unify error messages in rearrange_squash()

When the write opertion fails, we write that we could
not read. Change the error message to match the operation
and remove the full stop at the end.

When ftruncate() fails, we write that we couldn't finish
the operation on the todo file. It is more accurate to write
that we couldn't truncate as we do in other calls of ftruncate().

Signed-off-by: Ralf Thielow <ralf.thielow@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

sequencer.c

@@ -2926,9 +2926,9 @@ int rearrange_squash(void)
 		if (fd < 0)
 			res = error_errno(_("could not open '%s'"), todo_file);
 		else if (write(fd, buf.buf, buf.len) < 0)
-			res = error_errno(_("could not read '%s'."), todo_file);
+			res = error_errno(_("could not write '%s'"), todo_file);
 		else if (ftruncate(fd, buf.len) < 0)
-			res = error_errno(_("could not finish '%s'"),
+			res = error_errno(_("could not truncate '%s'"),
 					   todo_file);
 		close(fd);
 		strbuf_release(&buf);