Tweak 'svnadmin info' for packed FSFS.

* subversion/svnadmin/svnadmin.c
  (subcommand_info):
    Print "FSFS Packed Shards: %d/%d" if packing is possible, and say nothing
    if it is not possible.  A future revision might want to print something
    for each SVN_FS_FS__MIN_*_FORMAT constant that fs_format is ≥ than.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1483953 13f79535-47bb-0310-9956-ffa450edef68