[FOR DISCUSSION] Fixes client issue # 4178

This pull request is a fix for #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.  I've asked @rickbenetti how many files his project has to see if we can get away with just bumping it to 15,000 in fear that 50,000 may be too much.

I changed the limit to 100,000, however, and opened the top folder for mozilla-central (https://github.com/mozilla/mozilla-central) which has about 88,000+ files and it wasn't that much worse than the performance for 15,000 so maybe the performance penalty isn't worth worrying about.