Not sure if I'm on time for 1.5; Unicode 8 just got released.

Straighforward upgrade. Only changed maketables.go to prevent it from adding
the Cherokee upper and lower case mappings. This change causes the caseOrbit
table to NOT change. Added tests to verify that the relevant functions still
produce the correct result, even for Cherokee.

Fixes #11309

Change-Id: I42850f5b3399bde125b002efc78eff96dbd86a08
Reviewed-on: https://go-review.googlesource.com/11286Reviewed-by: Russ Cox <rsc@golang.org>