With this encoding flag, the object key-value pairs in output are in
the same order in which they were first inserted into the object.
To make this possible, a key of an object is now a serial number plus
a string. An object keeps an increasing counter which is used to
assign serial number to the keys. Hashing, comparison and public API
functions were changed to act only on the string part, i.e. the serial
number is ignored everywhere else but in the encoder, where it's used
to order object keys if JSON_PRESERVE_ORDER flag is used.
* Now that JSON_SORT_KEYS is implemented, take it into use with the
valid and valid-strip suites. This is to ensure that the tests
remain valid even if the string hash function is changed in the
future.
* Remove test_dump API test. Instead, implement the same tests more
elegantly in the encoding-flags suite.
