extract the merge of specs-index files into own class to allow
to process one stream after the other.
extract the manipulation of specs index files into its own class.
it is meant as create one when you need it and then throw it away.
this also means RubygemsGateway is now a little more then a factory
of ruby objects which have a java interface and has no more mutable
state.
fix api change after rebase
Merge pull request #779 from mkristian/remove-state-in-DefaultRubygemsGateway

Remove state in default rubygems gateway