Next time, remember to check with -Werror first...

These are usually internal to libc, and such symbols are exported in
the shared library on some platforms.

It may be problematic when compilers add new warnings over time.
./configure && make should always just work.

... and fix issues found.

This allows e.g. to use json_t in a header file that doesn't include
jansson.h:

    struct json_t;
    typedef struct json_t json_t;

    json_t *foo(json_t *bar);

Closes #95.

Issue #95.

Closes #97.

It didn't affect only the last element but all of them. One item too
much was always moved.

Uninitialized memory was read when the last item of a "full" array was
removed.

Support building and testing with VPATH.

Add -no-undefined to LDFLAGS

This tells libtool that jansson does not require any external symbols, and allows building it as a shared library (DLL) on Windows.

Mostly for symmetry reasons. Makes it easier e.g. to:

  int ok = 0;
  if(something)
      ok = 1;

  json_object_set_new(obj, "ok", json_boolean(ok));

Fixes #86.