Code simplification. No functional change.

* subversion/libsvn_repos/dump.c
  (svn_repos_dump_fs3): Rename the revision loop variable from 'i' to 'rev'
    and eliminate the 'to_rev' that exactly equalled it. Simplify the special-
    casing of revision 0. Move the 'from_rev' variable into a tighter scope.

git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1481171 13f79535-47bb-0310-9956-ffa450edef68