Revert ibrowse dependency to its original repository

This patch reverts the dependency on `ibrowse` to **v4.0.2** of its original repository. `ibrowse` has received a lot of fixes since it was forked by *Opscode*. The repository that `mini_s3` depends on has lagged behind and even contains an error in a format string in `ibrowse.erl`:

    src/ibrowse.erl:627: Warning: wrong number of arguments in format call

The main issue with this is that the original repository is still using `ets` tables. It's not clear to me whether the move to use a `dict` in the *Opscode* repository was really warranted or if it was just a precautionary measure.