__va_list_tag va_list[1];) which causes grief when attempting to reuse
va_list variables (eg, in vsnprintf retry loops). This is the reason for
MisterP's crashes as the pointers in va_list no longer point to valid data.
acinclude.m4:
shamelessly steal the va_list, va_copy and __va_copy macros from
cdda2wav but modified so AC_DEFINE includes the description (so
acconfig.h can remain gone)
configure.ac:
use AC_TYPE_VA_LIST, AC_FUNC_VA_COPY and AC_FUNC_VA__COPY
dstring.c:
stash the incoming va_list args in a temp var before calling vsnprintf
then restore them each time before retrying, but only if va_list is an
array (hopefully this is ok for when va_list is a structure)
