revset: make analyze() a separate step from optimize() This will allow us to evaluate unoptimized tree and compare the result with optimized one. The private _analyze() function isn't renamed since I'll add more parameters to it.

revset: extract tree transformation from optimize() This patch separates the simple tree transformation from the optimization step, which is called as _analyze() since I'll extend this function to infer ordering flags. I want to avoid making _optimize() more complicated. This will also allow us to evaluate unoptimized tree.