closes https://github.com/json-c/json-c/issues/278

Signed-off-by: Alexandru Ardelean <ardeleanalex@gmail.com>

Signed-off-by: Alexandru Ardelean <ardeleanalex@gmail.com>

I got this on Mac OS X at least.
Not sure if it shows up in other envs

error:
```
strerror_override.c:53:13: error: incompatible redeclaration of library function 'strerror' [-Werror,-Wincompatible-library-redeclaration]
const char *strerror(int errno_in)
```

Signed-off-by: Alexandru Ardelean <ardeleanalex@gmail.com>

Json object set xxx

Conflicts:
	tests/test_util_file.c

Conflicts:
	tests/test_util_file.c

The test is implied in test1.

The idea is to check that the returned lengths and strings
are identical to what is expected to return the already
tested function 'json_object_to_json_string_ext'.

Signed-off-by: José Bollo <jose.bollo@iot.bzh>

Also, be sure the right locale_t is freed if we fail on the second uselocale.
Finally, fix test_locale so it *doesn't* use json_object_to_json_string as
 that will simple re-emit the original parsed string values.

The function fstat isn't declared without this include
on debian strect/sid and Fedora-23

Change-Id: I660a32ff173dcba04674aed51ed855b4fa55ac67
Signed-off-by: José Bollo <jose.bollo@iot.bzh>

Fix issues with the test script so it works under distcheck too.

Add tests and descriptions for the functions in json_util.c

To better distinguish between entry->k and entry->v being const within linkhash, but non-const outside, add lh_entry_v() and lh_entry_k() accessors.
Make lh_entry->k const.

Change %d to %llu and add cast to unsigned long long for size_t arguments,
otherwise compilation will fail with errors like:

test1.c:70:15: error: format ‘%d’ expects argument of type ‘int’, but argument 2 has type ‘size_t {aka long unsigned int}’ [-Werror=format=]

%zu is avoided to stay compatible with old libc versions (like old Visual
Studio).

The user might want to use the userdata for something different, so the
serializer should ignore it by default.

Explicitly setting the serializer to json_object_double_to_json_string will
still make it interpret the userdata as a format string.

Add utility function for comparing json_objects

Tests added.

Do some basic checks on ints, doubles, strings, arrays and "complex" objects.

Tightening the number parsing algorithm

Some badly formated "numbers" could get partly parsed,
resulting in truncated results instead of raising an
error.

Examples :
 '1.2.3'      -> (double)1.2
 '2015-01-15' -> (int)2015

This patch is not perfect (ex: input can still end with a 'E', which
is forbidden by json.org doc) but should avoid non-sensically
formated input.

Tests added.

Add json_object_free_userdata() and json_object_userdata_to_json_string() too.