msvcrt: Add support for sprintf_s

[Chris Robinson]

This doesn't seem correct to me. According to MSDN, sprintf_s checks for valid 
formatting chars (in addition to the buffer and format arguments) and invokes 
an invalid parameter handler if something bad turns up. It then returns -1 
with errno set to EINVAL if execution is allowed to continue. Additionally, if 
the buffer is too small to hold the resulting string, it is made an empty 
string and invokes the invalid parameter handler. It also guarantees the 
output buffer is null terminated.

http://msdn.microsoft.com/en-us/library/ce3zzk1k(VS.80).aspx