[FOR DISCUSSION] Fixes client issue # 4178

We had agreed to bump the file indexer up to 50,000 but, after talking with @dangoor, the performance of quick open did start to feel sluggish around 15,000 so I capped it at 15,000.

However, I changed it to 100,000 and tried mozilla-central (https://github.com/mozilla/mozilla-central) which has 88,000+ files and it wasn't that much worse than 15,000 so maybe the performance penalty isn't worth worrying about.