Fix #283 - Refactor rsync to only use absolute paths

I really wonder if we should file a follow-up bug to convert this to a strategy where we create the `Buffer` at it's full size initially, then write/copy bits into it.  I'm unclear which is faster and/or more memory efficient between doing the concat algorithm and doing an initial create and then updating sections.  Probably a simple test with some quick profiling would help us get the answer.