mongodb/mongo — pull request #566 by dstorch (2013-12-04 21:38:49+00:00)
Title: SERVER-10026 git rid of $and match expressions with a single child

In some cases, the query planner used to leave filters in the query solution tree that were $and expressions with a single child. For instance, there might be a FETCH node whose filter is {$and: [{a: 3}]}. This change removes these extra $and match expression nodes (i.e. the FETCH filter will now simply be {a: 3}).