The standard requires both va_start and va_end to be called from the
same function. On the other hand, vsnprintf and vsprintf leave the
va_list on an undefined state according to the standard, so a copy must
be created before a second call to these functions.
- Removed trailing ';' from convenience macros.
- Convenience macros did not really need the ## __VA_ARGS__ extension.
Simply grouping all parameters into '...', while decreasing readability,
solves the portability issue.
- Added C99 check to dynstr.c.