Path Iterator

[arnaud-m]

• Provide an iterator over the paths of a subtree
• Restrict the iterator to paths for which the length is in a given range.

It should help for variables, constraints and graphics generation.

[arnaud-m]

Add additional tests :

• Compare node/link iterator to IDs
• Check consecutive indices for Rank Mapper

[arnaud-m]

Also provide ancestors iterator

[arnaud-m]

(dis)equality methods seem incorrect :

• test the current element
• but we do not test the iterated subgraph (past (?) and remaining elements)