This implementation allows to pack some FileEntryParsers together
and handle the case where to returned dirstyle isnt clearly defined.
The matching parser will be cached.
If the cached parser wont match due to the server changed the dirstyle,
a new matching parser will be searched.
Parses a line of an FTP server file listing and converts it into a usable
format in the form of an FTPFile instance. If the
file listing line doesn't describe a file, null should be
returned, otherwise a FTPFile instance representing the
files in the directory is returned.
listEntry - A line of text from the file listing
An FTPFile instance corresponding to the supplied entry