Rename eval function for Property Path Patterns

[hartig]

The spec contains two different functions called eval, one that defines the evaluation of property path patterns in Section 18.4 Property Path Patterns and one that defines the evaluation of algebra expressions in Section 18.5.2 Evaluation Semantics. As pointed out by @TallTed, one of them should be renamed. I think the first one (the one for PP patterns) is the natural candidate to be renamed. @afs proposed the name evalPath.