Fix hidden pattern references

[geoffp]

Addresses #469

Summary of changes:
This is frustratingly simple for how much time it took. Two main changes to the non-test code:

1. Make the pattern prefix matching regex aware of leading underscores in pattern file names.
2. Factor it out and write it only once.
3. Also, pre-calculate the verbose partial name in the Pattern object. I thought I could use it, but I couldn't (handlebars doesn't tolerate slashes in partial syntax)

And lots of unit tests to prove it. I created a place for shared code in the tests.

[bmuenzenmeyer]

fixed a merge conflict - going to test this manually too next free time i get - kids up now - dad time

[geoffp]

Groovy. Do that dad time!

[geoffp]

And, thanks for doing the merge. I picked exactly the wrong time to do stuff to unit tests.

[bmuenzenmeyer]

@geoffp does using lineage to go to the hidden pattern work for you?

It does not for me using this quick test above

[bmuenzenmeyer]

I'm okay making this a separate issue too if need be. Just curious what is happening on your end.

[geoffp]

@bmuenzenmeyer Just tested -- no, it's not working for me. Separate ticket?