text/encoding/charmap: a few bug fixes in global vars
text/encoding/charmap: a few bug fixes in global vars

- need pointer references to implement interface
- wrong constant assignments.

Change-Id: I3e5c77b70ea57ea7288c940c46e1c5db80047810
Reviewed-on: https://go-review.googlesource.com/8253
Reviewed-by: Nigel Tao <58ae08b3356928ff9c67562b4719487d54fe8348@golang.org>

cmars/tools,cmars/tools,cmars/tools,golang/text,cmars/tools,npchp110/text