Add json_object_free_userdata() and json_object_userdata_to_json_string() too.

Add const qualifiers to json_object_to_file and json_object_to_file_ext

Remove redefinition of strndup() which is no longer used in the codebase

Add extern to json_object_set_serializer so that it gets exported (Windows fix)

more strictness

fixing problem that isinf(-Inf) can be 1 or -1

Fix potential out-of-bounds read in json_tokener_error_desc

Found by Coverity. The number of elements of an array 'ar' is found by
sizeof(ar)/sizeof(ar[0]) and not sizeof(ar)

76const char *json_tokener_error_desc(enum json_tokener_error jerr)
 77{
 78        int jerr_int = (int)jerr;

1. Condition "jerr_int < 0", taking false branch

2. Condition "jerr_int > 112 /* (int)sizeof (gdal_json_tokener_errors) */", taking false branch
 79        if (jerr_int < 0 || jerr_int > (int)sizeof(json_tokener_errors))
 80                return "Unknown error, invalid json_tokener_error value passed to json_tokener_error_desc()";

CID 1076806 (#1 of 1): Out-of-bounds read (OVERRUN)3. overrun-local: Overrunning array "gdal_json_tokener_errors" of 14 8-byte elements at element index 112 (byte offset 896) using index "jerr" (which evaluates to 112).
 81        return json_tokener_errors[jerr];
 82}

filename should be passed as const char* to functions
json_object_to_file and json_object_to_file

Also adjust an error message in json_util to make it unique.  Fixes #87.

in strick mode, number must not start with 0

Support NaN and Infinity

Several MSVC fixes

Although JSON RFC does not support NaN or Infinity
as numeric values ECMA 262 section 9.8.1 defines
how to handle these cases as strings

int32_t is nowhere in msvc, so the version check could be even removed

one definition of json_object_object_foreach only works on c99 and later

Fix Broken Build, Check ADVANCE_CHAR

We forget to check or use the return value of the ADVANCE_CHAR macro,
and upon compilation an error is thrown because of its lack of use. This
patch checks to see if the macro was successful, and if not replaces the
offending character with a replacement.

While parsing token data, we use the POP_CHAR macro to 'peek' at
character data. This behaviour is noted in the comments for the macro,
yet the definition is left as 'pop'. Changing to PEEK_CHAR does not
imply that the character being observed is removed.

rename AM_CONFIG_HEADER to AC_CONFIG_HEADER

the former has been deprecated and does not work on newer autoconf
versions.