No need for that array to be mutable
Hit the disk system less when finding an index's last mod date
Use Debug config for profiling

This ensures symbols are not desymbolicated, and makes it easier to find your way through the code
(Note: correct solution would be to set up using .dsym - Issue #1610)
Add a new URLByReallyResolvingSymlinksInPath method

Apple's equivalent doesn't resolve all paths (e.g. /tmp, /etc and /var)