Added unit tests for the "file-copy" function.
Added unit tests for the "file-exists?" function.
Added unit tests for the "file-is-dir?" function.
Code cleanups.
Cleaned up handling of SObjSymbol lists on TOS internals.
Added unit tests for the "file-is-regular?" function.
Added unit tests for the "file-join" function.
Added unit tests for the "file-mkdir" function.