Sync FS Reads/Writes

Previously, in certain environments, FS caching may have prevented artifact modifications from being seen by later stages of a deploy script. Particularly, it lead to spurious deployment failures claiming that a contract had unlinked library references, when it in fact had been linked just prior.

As of this release, all file I/O is explicitly performed with O_SYNC, which, while marginally slower, is much more robust in the face of questionable FS caching implementations.