language: bug fix in compact index number

Compensate for the fact that "und" was already taken out.
Also changed the checksum computation to reflect this change.

Change-Id: I2b29df2a41cd186d886628390a55bd19d0175075
Reviewed-on: https://go-review.googlesource.com/14750
Reviewed-by: Nigel Tao <nigeltao@golang.org>
2 files changed