#1 Miscellaneous fixes to file selector functions for Linux and OSX

First commit: * Escape parameters correctly on Linux/OSX * Prevent warnings about `-maxdepth 1` not being in the correct position * Prepare the code for better quoting of Windows parameters in future * Prepare the code for an option to include hidden files in listings in future Second commit: * Properly handle files with LFs in the name. Under Linux, any character is possible for a filename except `/` and ASCII `NUL` (`'\000'`). Third commit: * The default "All Files" mask did not show files without dots. This commit corrects it. Fourth commit: * Fix crash in demo when selecting a file instead of a directory, via OpenDirectory