WP Filesystem changes

[DD32]

Just a few changes/enhancements/bugfixes for the Filesystem Abstraction classes.

• Bring the FTP Constants inline with find_folder() - Moves all the processing for the various folders to a single function, much easier to handle
• Changes the folder locations from WP_Filesystem to -always- return a trailing slash, This is for maximum compatibility with all host setups, ie. abspath == ftp foot == /, In the current setup, it can end up using a path such as which causes some problems with some setups
• Lots of formatting cleanups
• Return a standardised chmod return values for all classes, May need further testing, But given each class was returning something different, and Core isnt using it, I'm pretty certain its a safe change
• return false on attempting to delete a empty path - If a bug occurs, and something asks to delete "null" or "" then prevent it from deleting, some take this to mean delete "." or "/"
• (FTP) Better support for listing for a single file in a directory (ie. /wordpress/.maintanence)

[ryan]

(In [10919]) WPFS cleanups. Props DD32. fixes #9525

[ryan]

See #9535

[ryan]

(In [10930]) Revert FTP parts of [10919]. fixes #9535 see #9525