Evaluating current path inside of a loop

Following on from a conversation on the user group [1] I believe it is currently not possible to correctly evaluate the current path inside the body of a loop.

The patch included in this pull request addresses this issue, though I'm not sure if it meets coding guidelines for this project. Please advise on any style or api updates that are required I'd be happy to address them to get this patch incorporated.

[1] https://groups.google.com/forum/?fromgroups#!topic/gremlin-users/iKKUFSwfP0Y