[BUGFIX] Avoid "too many open files" exception during I18n filesystem scan
The I18n Service scans the filesystem for localized files in order to build
a list of available locales, this is done with a RecursiveIterator, which
will keep handles open in nested structures. A simple stack like now
used in the FileMonitor prevents the problem of "too many open files"
(leading to a fatal error) and at the same time brings clear performance
boost. Additionally hidden directories and files (starting with ".") are
Releases: master, 3.0, 2.3