Note that we pass va_list pointers around instead of just va_lists, which
would seem more intuitive. This is necessary since the behaviour of va_lists
passed as function parameters is finicky. Quoth stdarg(3):
If ap is passed to a function that uses va_arg(ap,type) then the value
of ap is undefined after the return of that function.
The pointer-passing strategy is used by Python's Py_BuildValue() for the same
purpose.
This patch adds two new fields to the json_error_t struct: column and
source. It also adds functions to populate json_error_t internally.
The column field is not currently used, but it will be utilized in the
decoder and pack/unpack functions.
After looking at the new code for a few days, I didn't like it
anymore. To prepare for the future, a few fields will be added to the
json_error_t struct later.
This reverts commit 23dd078c8d. Some
adjustments were needed because of newer commits.
