The rbt land command can now land review requests recursively; that

is, it can now land all the unlanded review requests in the same

repository that the review request depends on. It also does this in

the correct order so that they should apply successfully.
This is accomplished by building a dependency graph of the review

request and generating a topological sorting of this graph. The

reversed topological sorting yields a correct order for landing the

dependant review requests. This is because the relationship that

determines what to land first is blocking. A reversed topological

sorting of the dependency graph is a valid topological sorting of the

blocking graph (as the blocking graph is the transpose graph of the

dependency graph).
Graph utilities have been added in rbtools.utils.graphs for

traversing a graph in depth-first order, generating a topological

sort, and determining if a path exists between two vertices in a

graph.

Succesfully landed https://reviews.reviewboard.org/r/7323 and all of

its dependencies recursively.