ENH+FIX: Read all meas info, fix raw concat error, add viz.compare_fiff()

This PR reads the missing meas_info (#310). Could be made more useful by actually parsing the blocks instead of storing them in memory -- I'm open to doing that if people think it would be useful.

Also fixed an error with not setting `raw.fids` properly on `raw.copy()`, with a test that failed without the appropriate change.