Improve log message on 3.2 when downgrading from 3.3+ after creating new WT index

dan:(git)mongo[master]/$ ../3.2-mongo/mongod

2016-04-27T12:48:18.658-0400 I CONTROL  [initandlisten] MongoDB starting : pid=28134 port=27017 dbpath=/data/db 64-bit host=dan

2016-04-27T12:48:18.658-0400 I CONTROL  [initandlisten] db version v3.2.5-33-g111b51d

2016-04-27T12:48:18.658-0400 I CONTROL  [initandlisten] git version: 111b51db9db315b6ed0fcfc8f444c75c85f54dc6

2016-04-27T12:48:18.658-0400 I CONTROL  [initandlisten] allocator: tcmalloc

2016-04-27T12:48:18.658-0400 I CONTROL  [initandlisten] modules: none

2016-04-27T12:48:18.658-0400 I CONTROL  [initandlisten] build environment:

2016-04-27T12:48:18.658-0400 I CONTROL  [initandlisten]     distarch: x86_64

2016-04-27T12:48:18.658-0400 I CONTROL  [initandlisten]     target_arch: x86_64

2016-04-27T12:48:18.658-0400 I CONTROL  [initandlisten] options: {}

2016-04-27T12:48:18.675-0400 I -        [initandlisten] Detected data files in /data/db created by the 'wiredTiger' storage engine, so setting the active storage engine to 'wiredTiger'.

2016-04-27T12:48:18.675-0400 I STORAGE  [initandlisten] wiredtiger_open config: create,cache_size=74G,session_max=20000,eviction=(threads_max=4),config_base=false,statistics=(fast),log=(enabled=true,archive=true,path=journal,compressor=snappy),file_manager=(close_idle_time=100000),checkpoint=(wait=60,log_size=2GB),statistics_log=(wait=0),

2016-04-27T12:48:18.877-0400 I CONTROL  [initandlisten]

==> 2016-04-27T12:48:18.879-0400 I -        [initandlisten] Fatal assertion 28579 UnsupportedFormat: Application metadata for table:index-0-1896016118062454958 has unsupported format version 7

2016-04-27T12:48:18.879-0400 I -        [initandlisten]

***aborting after fassert() failure