Support generic Hadoop Compatible Filesystem

This is a shortened version of PR #358, with focus on filesystem only.
https://github.com/apache/hadoop-common/blob/release-1.0.4/src/core/org/apache/hadoop/conf/Configuration.java#L199

As long as the files are in the classpath, we are good.  Can you explain the case you are trying to solve?  The only difference between the impls that I see is the class loader used.  Since we expect to control the runtime, both ClassLoaders will be the same.