More FTP work

[DonLakeFlyer]

• Restructured code to flatten class hierarchy and support unit testing
• Refactored command opcodes and error codes. Largest change is instead of trying to return a pack of descriptive error codes for the various file system related commands. If a file system command fails, kErrFailErrno is returned, with the errno from the call in data[2]. Then the client can decide how fancy they want to get with error handling/display.
• Added support for create/remove directory and create file. (Only missing command now is write file)
• Added comprehensive unit tests for all of the above
• Fixed bugs found by the unit test
• Improved unit test support code

For code review, best viewed as completely new files intend of trying to make sense of the diff.

[vooon]

My thoughts:

1. Set kRspAck = 128 (so we could add kCmd's with backwards compatibility)
2. Add field uint8_t rsp_opcode for return original request opcode in kRspAck/kRspNak (i think it should be between size and padding).
3. Remove crc32 calculation (just not to loose)

[vooon]

Also need command to open file for write (not creat()) with random write access.

So i can do something like this:

int fd = open("remote/file", 0);
write(fd, "my data1", 8);
lseek(fd, 4, SEEK_SET);
write(fd, "ata2", 4);