CAMEL-5269: Allow file/ftp producer to use overrule filename header to use for writing file name, and throwaway after use, and preserve original filename header. Makes it easier to keep same file name and write to an endpoint using a different name.

git-svn-id: https://svn.apache.org/repos/asf/camel/trunk@1440560 13f79535-47bb-0310-9956-ffa450edef68