test: add test for fixed issue 7863
test: add test for fixed issue 7863

Fixes Issue 7863

LGTM=rsc
R=rsc, ruiu
CC=golang-codereviews
https://codereview.appspot.com/98610045

pombredanne/go-deleteme,pombredanne/go-deleteme,pombredanne/go-deleteme,pombredanne/go-deleteme,tv42/old-go,tv42/old-go,tv42/old-go,tv42/old-go,tv42/old-go,tv42/old-go,pombredanne/go-deleteme,pombredanne/go-deleteme,tv42/old-go,pombredanne/go-deleteme