FtpOperations Delete operation not respecting Stepwise Attribute

Current implementation of deleteFile(String name) ignores the Endpoints 'stepwise' requirement.

This was noticed when interfacing with a MVS ftp system with the operation failing silently as the resulting exception is swallowed by higher order code.

I've unfortunately been unable to create a test case that emulates the behavior, since the Apache FtpServer and associated mocks used within the test cases don't emulate the behavior of the MVS platform.

I believe other operations suffer the same problem (e.g rename).

I've attached a patch that corrects the issue. Existing test cases all pass, though someone will probably want to see if this implementation is the most efficient.