'svnadmin hotcopy --incremental' is currently broken for FSFS format 6
repositories due to unpacked revprops not being cleaned up after copying
revprop packs.

This patch will cause the respective test use format 6 and FAIL.

* subversion/tests/cmdline/svnadmin_tests.py
  (hotcopy_incremental_packed): use latest repo format


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1512300 13f79535-47bb-0310-9956-ffa450edef68
Fixing 'svnadmin hotcopy --incremental' for FSFS format 6 repositories.
Delete non-packed revprops after their packed counterparts have been
copied.

* subversion/libsvn_fs_fs/fs_fs.c
  (hotcopy_remove_files): similar to hotcopy_remove_rev_files but
                          takes the shard parent folder as parameter,
                          i.e. works for revs and revprops alike
  (hotcopy_remove_rev_files): call the above
  (hotcopy_remove_revprop_files): new, similar function
  (remove_folder): new utility function
  (hotcopy_incremental_check_preconditions): 
  (hotcopy_body): remove revprop files after packing just the same
                  as rev files

git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1512301 13f79535-47bb-0310-9956-ffa450edef68