On the fsfs-format7 banch:  Add tests for the new fsfs-internal
string table data structure.

* build.conf
  (string-table-test): new build target
  (libs): add new test as dependency

* subversion/tests/libsvn_fs_fs/string-table-test.c
  (): new file
  (STRING_COUNT,
   basic_strings): input data
  (generate_string): utility method
  (create_empty_table,
   short_string_table,
   large_string_table,
   many_strings_table): individual tests
  (test_funcs): register tests


git-svn-id: https://svn.apache.org/repos/asf/subversion/branches/fsfs-format7@1451736 13f79535-47bb-0310-9956-ffa450edef68