core: introduce future::forward_to()
core: introduce future::forward_to()

It causes that when future is resolved, the target promise will be
resolved too with the same state.

rentongzhang/scylla,shyamalschandra/seastar,jonathanleang/seastar,scylladb/scylla,guiquanz/scylla,stamhe/scylla,scylladb/scylla-seastar,norcimo5/seastar,kjniemi/scylla,bzero/seastar,victorbriz/scylla,phonkee/scylla,capturePointer/scylla,syuu1228/seastar,stamhe/scylla,ducthangho/imdb,tempbottle/seastar,kjniemi/scylla,duarten/scylla,flashbuckets/seastar,kjniemi/seastar,aruanruan/scylla,avikivity/seastar,joerg84/seastar,linearregression/scylla,kangkot/scylla,wildinto/seastar,cloudius-systems/seastar,senseb/scylla,respu/scylla,justintung/scylla,asias/scylla,linearregression/seastar,joerg84/seastar,wildinto/scylla,acbellini/scylla,eklitzke/scylla,dreamsxin/seastar,gwicke/scylla,shyamalschandra/seastar,avikivity/seastar,sjperkins/seastar,duarten/scylla,gwicke/scylla,tempbottle/scylla,leejir/seastar,raphaelsc/scylla,kjniemi/seastar,chunshengster/seastar,mixja/seastar,scylladb/scylla,mixja/seastar,stamhe/seastar,stamhe/scylla,rentongzhang/scylla,bowlofstew/seastar,bowlofstew/scylla,raphaelsc/seastar,kangkot/scylla,capturePointer/scylla,guiquanz/scylla,koolhazz/seastar,tempbottle/seastar,dwdm/scylla,victorbriz/scylla,acbellini/seastar,acbellini/scylla,shyamalschandra/seastar,justintung/scylla,senseb/scylla,bowlofstew/scylla,dreamsxin/seastar,guiquanz/scylla,sjperkins/seastar,acbellini/seastar,scylladb/seastar,bowlofstew/scylla,tempbottle/scylla,ducthangho/imdb,anzihenry/seastar,rentongzhang/scylla,bzero/seastar,scylladb/scylla-seastar,hongliangzhao/seastar,kangkot/scylla,eklitzke/scylla,mixja/seastar,scylladb/scylla,xtao/seastar,dwdm/seastar,kjniemi/scylla,kjniemi/seastar,leejir/seastar,rluta/scylla,wildinto/scylla,raphaelsc/scylla,cloudius-systems/seastar,aruanruan/scylla,flashbuckets/seastar,scylladb/seastar,linearregression/scylla,glommer/scylla,wildinto/seastar,gwicke/scylla,dwdm/seastar,victorbriz/scylla,joerg84/seastar,tempbottle/seastar,linearregression/scylla,avikivity/seastar,bowlofstew/seastar,syuu1228/seastar,rluta/scylla,ducthangho/imdb,dwdm/scylla,raphaelsc/seastar,duarten/scylla,printedheart/seastar,leejir/seastar,linearregression/seastar,flashbuckets/seastar,acbellini/scylla,wildinto/seastar,printedheart/seastar,raphaelsc/seastar,printedheart/seastar,anzihenry/seastar,sjperkins/seastar,glommer/scylla,glommer/scylla,wildinto/scylla,jonathanleang/seastar,chunshengster/seastar,bowlofstew/seastar,norcimo5/seastar,shaunstanislaus/scylla,dreamsxin/seastar,asias/scylla,norcimo5/seastar,raphaelsc/scylla,aruanruan/scylla,shaunstanislaus/scylla,justintung/scylla,xtao/seastar,avikivity/scylla,capturePointer/scylla,scylladb/scylla,asias/scylla,koolhazz/seastar,slivne/seastar,linearregression/seastar,acbellini/seastar,stamhe/seastar,jonathanleang/seastar,phonkee/scylla,phonkee/scylla,bzero/seastar,chunshengster/seastar,anzihenry/seastar,koolhazz/seastar,respu/scylla,respu/scylla,senseb/scylla,xtao/seastar,tempbottle/scylla,cloudius-systems/seastar,hongliangzhao/seastar,rluta/scylla,avikivity/scylla,slivne/seastar,dwdm/scylla,shaunstanislaus/scylla,stamhe/seastar,slivne/seastar,eklitzke/scylla,syuu1228/seastar,hongliangzhao/seastar,scylladb/seastar,scylladb/scylla-seastar,dwdm/seastar,avikivity/scylla