Turn ros_comm customizations into a separate package?

[peci1]

Hi, your customization regarding a more efficient index for rosbags looks definitely very interesting. However, using a fork of ros_comm is problematic for most users, as it is harder to get updates from upstream. Do you think it'd be possible to make the changes in a separate package, e.g. rosbag_fast or a similar name? The Python part should be quite easy as it should be sufficient to monkey-patch the original rosbag functions you need to change.

The C++ part might be problematic, but there could possibly be a solution (as a possible workaround I can see for example that the index file would report itself as rosbag version 99 or so, and would contain a link to the original bag file, and if you'd like to open the bag with the fast index, you would pass just the index file, rosbag would open it and read with a reader for version 99, and internally it would read the fast index and open the original bag file).