Add AFlags parameter to TIdStack for Receive(), ReceiveFrom(), ReceiveMsg(), Send(), and SendTo()

[rlebeau]

Add an AFlags parameter to TIdStack and descendants for the Receive(), ReceiveFrom(), ReceiveMsg(), Send(), and SendTo() methods. This way, callers can use flags like PEEK, WAITALL, etc.

TIdStackBSDBase and descendants have such an AFlags parameter for their lower-level wrappers for the platform API recv(), recvfrom(), send(), and sendto() functions, but that parameter is not exposed in TIdStack so it can be passed down the chain.