On the fsfs-improvements branch:  Rename svn_fs_fs__write_revnum_file
to reflect its actual purpose and document it properly

* subversion/libsvn_fs_fs/util.h
  (svn_fs_fs__write_revnum_file): rename this ...
  (svn_fs_fs__write_min_unpacked_rev): ... to this; fix docstring

* subversion/libsvn_fs_fs/util.c
  (svn_fs_fs__write_revnum_file): rename implementation ...
  (svn_fs_fs__write_min_unpacked_rev): ... as well

* subversion/libsvn_fs_fs/hotcopy.c
  (hotcopy_copy_packed_shard): update caller

* subversion/libsvn_fs_fs/pack.c
  (pack_shard): update caller

Found by: danielsh

git-svn-id: https://svn.apache.org/repos/asf/subversion/branches/fsfs-improvements@1510344 13f79535-47bb-0310-9956-ffa450edef68