doc: fix happens-before rules for buffered channels
The current wording is reversed in 2 places.
Not sure how it got 4 LGTMs (mine was there as well).
Update issue 6242.

LGTM=dan.kortschak, r, rsc
R=golang-codereviews, 0xjnml, dan.kortschak, r, rsc
CC=golang-codereviews
https://codereview.appspot.com/101980047
cmd/cgo: for typedef of untagged struct, use typedef name in C code

Fixes issue 8148.

LGTM=cookieo9, rsc
R=rsc, cookieo9
CC=golang-codereviews
https://codereview.appspot.com/103080043