Pin the FSFS f7 item type to a fixed-length data type.
Make sure we use that type consistently.

* subversion/libsvn_fs_fs/index.h
  (svn_fs_fs__p2l_entry_t): Fix the item type to 32 bits which is way
                            more than we'll ever need and which aligns
                            nicely with the rest of the struct.

* subversion/libsvn_fs_fs/index.c
  (read_entry): Remove unnecessary type conversion.

* subversion/libsvn_fs_fs/cached_data.c
  (dbg_log_access): Always use uint32 to hold item types.

* subversion/libsvn_fs_fs/transaction.c
  (write_container_rep,
   write_container_delta_rep,
   write_final_rev): Same.

git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1627966 13f79535-47bb-0310-9956-ffa450edef68