Ok I've fixed this issue now - turned out to be really simple. I've also added a File.getSize() function and a FileSystem.descriptionOfSizeInBytes() (Maybe this function should be part of the File class but I couldn't get it to work unless it was called on a file object which shouldn't be necessary). These are wrappers for the JUCE functions of the same name.
I've also added a wrapper function to generate a SHA256 has from a file, might be useful for verifying the integrity of downloaded files.
I noticed that the autocomplete popup doesn't seem to work for File. in the latest version, anyone else having this issue?