Update how global variables are matched

[brianherold]

I was surprised how many global variables this found in the codebase I'm working in, so I looked into it. Turns out some of the globals it found weren't actually globals, and it missed some actual globals.

I added test cases for the 4 types of missing or false globals I found, then updated the code to pass the tests.

[brianherold]

I found a few other false global variables, so I pushed some additional code changes.