[libqb] Incorrect definition of va_copy

[Виноградов Василий]

In qbdefs.h there's the following definition:

#if defined (__GNUC__) && defined (__STRICT_ANSI__)
#define va_copy(_a, _b) *_a = *_b
#endif /* ANSI */

As a result libqb fails with segmentation fault on Debian wheezy. I think it would be more
correct to define va_copy as follows:

#if ! defined (va_copy) && defined (__va_copy)
#define va_copy(_a, _b) __va_copy(_a, _b)
#else
#define va_copy(_a, _b) *_a = *_b
#endif