When a user renames a file to "__test.txt" (two underscores or more),
then FileNameFilter will only remove the very first underscore from the
filename. This is not sufficient, as any number of underscores in the
filename will be problematic when Filesystem::sync() is called, it will
remove that File record thinking it's an internal file. This fixes it
so any number of underscores are stripped out at the start of the filename.
The intl extension in PHP 5.4 provides a Transliterator class, which
conflicts with the SilverStripe one. This leads to some really weird
ReflectionExceptions about Transliterator's constructor being
private.
ENHANCEMENT New FileNameFilter class for a more customisable way to influence filename filtering in Upload->load(), Folder->addUploadToFolder() or Image->loadUploadedImage()
