Capture task dependency tree, along with graph

[khuck]

Currently, APEX only captures the task dependency graph. It would be nice to capture a task dependency tree. While admittedly larger, it would allow analysis of specific code / dependency paths through the application (with less annotation required).

To capture the graph, only the task parent is recorded. To capture the tree, the parent node in the dependency tree would also be captured. Upon task creation, a new node in the tree would be created. The tree would be rooted at APEX_MAIN.

Graph example (A calls B and E, which both call C):

A -> B -> C -> D
 \-> E ->/

Tree example (A calls B and E, which both call C):

A -> B -> C -> D
 \-> E -> C -> D

[khuck]

Fixed with 9b89b30