85b7463change def of reducer to take function ptrfe6366eadd engine basea98720emore deps git-subtree-dir: subtree/rabit git-subtree-split:85b746394e
85b7463change def of reducer to take function ptrfe6366eadd engine basea98720emore deps git-subtree-dir: subtree/rabit git-subtree-split:85b746394e