Clean up the code in json_object_new_* a bit by dropping unnecesary json_object_base variables.

The current changes split out _only_ json_type_object, and thus have a number of hacks
 to allow the code to continue to build and work.

Originally  mentioned in issue #535.
When complete, this will probably invalidate #552.
This is likely to cause notable conflicts in any other significant un-merged
changes, such as PR#620.

A custom double formatter can lead to truncation of the rest of the
JSON document.

If a custom formatter completely fills the buffer used by snprintf
with a trailing dot or comma and the formatting option
JSON_C_TO_STRING_NOZERO has been specified, then an iterator moves
past the ending '\0' (off-by-one buffer overflow) to set an
additional '\0' and adds the first '\0' into the printbuf.

Since '\0' will eventually be considered the terminating character
of the complete printbuf result, all trailing characters are lost.

This leads to an incomplete JSON string as can be seen with the
test case.

The off-by-one can be noticed if compiled with address sanitizer.

Since this is a very special case and a malformed formatter could
do way more harm and is the responsibility of the user of this
library, this is just a protective measure to keep json-c code as
robust as possible.

Fix compiler errors and warnings when building on IBM operating systems such as AIX and IBM i.

introduced in #542
fixes #601

Add a test to check for this too.

Increase coverage

Test coverage for json_c_version.

modify json-c default build type, and fix up the assert() errors in t…

validate utf-8 string

cc -DHAVE_CONFIG_H -I. -I..  -I.. -I../tests    -O2 -pipe  -fstack-protector-strong -fno-strict-aliasing  -Wall -Werror -Wcast-qual -Wno-error=deprecated-declarations -Wextra -Wno-unused-parameter -D_GNU_SOURCE -D_REENTRANT -MT test_parse.o -MD -MP -MF .deps/test_parse.Tpo -c -o test_parse.o test_parse.c
test_parse.c:256:14: error: adding 'int' to a string does not append to the string [-Werror,-Wstring-plus-int]
        { "null123" + 4,       4, 3, json_tokener_success, 1 },
          ~~~~~~~~~~^~~
test_parse.c:256:14: note: use array indexing to silence this warning
        { "null123" + 4,       4, 3, json_tokener_success, 1 },
                    ^
          &         [  ]
test_parse.c:258:12: error: adding 'int' to a string does not append to the string [-Werror,-Wstring-plus-int]
        { "nullx" + 4,         2, 0, json_tokener_error_parse_unexpected, 1 },
          ~~~~~~~~^~~
test_parse.c:258:12: note: use array indexing to silence this warning
        { "nullx" + 4,         2, 0, json_tokener_error_parse_unexpected, 1 },
                  ^
          &       [  ]
test_parse.c:260:25: error: adding 'int' to a string does not append to the string [-Werror,-Wstring-plus-int]
        { "{\"a\":1}{\"b\":2}" + 7,
          ~~~~~~~~~~~~~~~~~~~~~^~~
test_parse.c:260:25: note: use array indexing to silence this warning
        { "{\"a\":1}{\"b\":2}" + 7,
                               ^
          &                    [  ]
3 errors generated.
*** Error code 1

Stop.

Increased the test coverage of printbuf.c 82% to 92%.

update pointer test case

update tsetcase for tokener_c

update json_visit testcase