allow relative paths to be created inside archives.

This jira is a shadow jira for mapreduce changes related to HADOOP-3663.
Archives currently stores the full path from the input sources - since it allows multiple sources and regular expressions as inputs. So the created archives have the full path of the input sources. This is un intuitive and a user hassle. We should get rid of it and allow users to say that the created archive should be relative to some absolute path and throw an excpetion if the input does not confirm to the relative absolute path.