LU-1904 idl: add checks for OBD_CONNECT flags

LU-1904 idl: add checks for OBD_CONNECT flags

Make it harder to accidentally declare OBD_CONNECT flags without
properly defining their names.  Otherwise, this can cause serious
compatibility problems if two features are using the same flag.

Add the definition lines into spelling.txt so there is *always*
a warning generated, since this always needs proper attention.

Make it clear whom to contact when reserving a new feature flag.

Test-Parameters: trivial
Signed-off-by: Andreas Dilger <adilger@whamcloud.com>
Change-Id: I9a5e2c97c40c39ea57d20979d4b130854edc785a
Reviewed-on: https://review.whamcloud.com/48053
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Lai Siyao <lai.siyao@whamcloud.com>
Reviewed-by: Sebastien Buisson <sbuisson@ddn.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>