Various Changes to afc.py

+ AFCError won't fail when an unkown error code is used.
+ AFCFile should've used AFCClient instead of creating its own in the
first place.
+ AFCFile supports newline conversion (no support for Mac OS 9,
__init__.py throws an error anyway).
+ Since Jython is written in Java, and LBYL is prefered in Java world, I
assumed it would be better in terms of performance. Surprisingly, EAFP
is faster in Jython too.
+ Renamed functions: "file_remove" and "file_rename", to "remove_path"
and "rename_path", since both functions can be used for directories as
well.
+ Fixed file_tell and dir_walk
+ Used posixpath.join whenever it was possible