Don't shadow the builtin 'zip'.

Auditors: pl
Refactor junit test discovery code.

Mostly renaming this to make it clearer what's going on.

Auditors: pl
Replace a filter with a list comprehension.
Style nits.
Fix a zinc analysis filtering bug.

jar references are in binary deps in zinc analysis files, not external deps.
External deps are for src->class deps to upstream classes.

Auditors: pl

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