Use work effort instead of total to compute revenue

total_effort contains the effort of the children but sum_tree needs only the
value of the work without the children.

review2931003
(transplanted from ce55336d85d1d81e1117ace09f851edbac98f228)

--HG--
extra : transplant_source : %CEU3m%85%D1%D8%1E%11%17%AC%E0%9F%85%1E%DB%AC%98%F2%28