GlobalConfig: Actually current section from getLogSection()

It was returning the value of an unused member 'currentLogSection'
instead of the end of the log section stack.
GlobalConfig: Setting 'debug=false' will turn off debug mode

It was an incomplete implementation that toggled it on but with
no way to turn it off (short of clearing the session cookie).
gitignore: Add cache/

The cache/ directory is the recommended target of FileCacheBackend
when used developing locally.
Clean up exception handling and improve debug logging
Request: Remove deprecated 'exists' and 'getBool' methods