On the fsfs-format7 branch:  Use the new Packed Data API to serialize /
deserialize string tables.  Duplicate the string table tests such that
the second variant will write & read the data before checking it.

* subversion/libsvn_fs_fs/string_table.h
  (svn_fs_fs__string_table_builder_estimate_size,
   svn_fs_fs__write_string_table,
   svn_fs_fs__read_string_table): declare new private API

* subversion/libsvn_fs_fs/string_table.c
  (builder_table_t): track total size of long string data
  (string_sub_table_t): use the right element data type
  (svn_fs_fs__string_table_builder_add): maintain new tacking info
  (svn_fs_fs__string_table_builder_estimate_size): implement
  (create_table): formatting fix
  (svn_fs_fs__write_string_table,
   svn_fs_fs__read_string_table): implement using the new packed data API

* subversion/tests/libsvn_fs_fs/string-table-test.c
  (store_and_load_table): new utility function
  (create_empty_table,
   short_string_table,
   large_string_table,
   many_strings_table): rename to *_body and add do_load_store flag;
                        add tests with orig. names that call the bodies
  (store_load_short_string_table,
   store_load_large_string_table,
   store_load_empty_table,
   store_load_many_strings_table): new tests calling the same body
  (test_funcs): register new tests


git-svn-id: https://svn.apache.org/repos/asf/subversion/branches/fsfs-format7@1462007 13f79535-47bb-0310-9956-ffa450edef68