icebergs: Updates to avoid id roll-over

- NOAA-GFDL/icebergs@c67f435 Fixes hang when mpp_io is not called on some PEs with empty berg restarts
- NOAA-GFDL/icebergs@a527054 Merge pull request mom-ocean#51 from adcroft/id-fix-for-32-bit
- NOAA-GFDL/icebergs@f7988fe Removed last vestiges of %iceberg_num
- NOAA-GFDL/icebergs@be47643 Read id from restarts or generate ids if iceberg_num is present
- NOAA-GFDL/icebergs@08ea446 Split convert_old_id() in cij_from_old_id()
- NOAA-GFDL/icebergs@3038a47 Start grd%iceberg_counter at 0 and increment before generating berg
- NOAA-GFDL/icebergs@df4e43a Add id to write_restart()
- NOAA-GFDL/icebergs@22bb2a0 Removed read_restart_bergs_orig()
- NOAA-GFDL/icebergs@32eba0a Use %id instead of $iceberg_num
- NOAA-GFDL/icebergs@04e827b Fix id_from_2_ints() for Intel and PGI
- NOAA-GFDL/icebergs@1efcdaf Use %id in all print statements
- NOAA-GFDL/icebergs@bbde6c2 Set %id everywhere %iceberg_num is set
- NOAA-GFDL/icebergs@a5d3576 Use push/pull_buffer_value() in pack_traj_into_buffer2()
- NOAA-GFDL/icebergs@905f4f2 Modularized generate_id(), added convert_old_id()
- NOAA-GFDL/icebergs@c8d5b63 Re-factor pack_berg_into_buffer2()
- NOAA-GFDL/icebergs@85dfb93 Removed use/public lines for pack_berg_into_buffer2
- NOAA-GFDL/icebergs@2ec7bd0 Merge branch 'fix-empty-restart-files' into id-fix-for-32-bit
- NOAA-GFDL/icebergs@04dfea1 Fix for when restart files have zero bergs
- NOAA-GFDL/icebergs@e7fc83f Set berg%id everywhere %iceberg_num is set
- NOAA-GFDL/icebergs@33e090d Added function generate_id()
- NOAA-GFDL/icebergs@0348755 Add functions id_from_2_ints() and split_id()