On the fsfs-format7 branch: prevent hiding "index" identifier warning.

* subversion/libsvn_fs_fs/changes.h
  (svn_fs_fs__changes_get_list): rename parameter "index" to "idx"


git-svn-id: https://svn.apache.org/repos/asf/subversion/branches/fsfs-format7@1467474 13f79535-47bb-0310-9956-ffa450edef68