Extend the FSFS f7 "fuzzy" test such that we change any byte in any
revision  of the "greek" repo individually to any value.

Any change that affects the actual contents shall be detected.  The only
undetected changes are allowed in parts of the index data that does not
affect the interpretation of the index in our case.

* subversion/tests/libsvn_fs_fs/fs-fs-fuzzy-test.c
  (fuzzing_1_byte_1_rev): New sub-function, mainly factored out from
                          fuzzing_1_byte_test.  Allows us to test any
                          given revision and determines whether a
                          change is detectable.                     
  (fuzzing_1_byte_test): Use the new sub-routine to test all revisions
                         instead of the just rev 1.  Also, accept a
                         more flexible modifier function.

  (set_byte): New modifier function.
  (fuzzing_set_byte_test): New test core function that will that runs
                           the modification test for a given range of
                           byte values.

  (invert_byte,
   fuzzing_invert_byte_test,
   increment_byte,
   fuzzing_increment_byte_test,
   decrement_byte,
   fuzzing_decrement_byte_test,
   null_byte,
   fuzzing_null_byte_test): Update the existing tests to use the new
                            modifier callback signature.

  (FUZZING_SET_BYTE_TEST_N,
   TEST_FUZZING_SET_BYTE_TEST_N): New macros to generate test functions
                                  for all byte value ranges.
  (FUZZING_SET_BYTE_TEST_N(*)): Instantiate tests.
  (max_threads): Allow for unlimited parallelism.
  (test_funcs): Add the new test cases.

git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1631198 13f79535-47bb-0310-9956-ffa450edef68