Also add checking for "would block" errors in send() and receive().
Check for set nonblocking failures in TCPConnector as well (generate warnings rather than errors)
The StringRef class does not ensure the string is null terminated. As there is
no defined way to actually check for a null terminator, we determine
if it is null terminated based on the constructor type. Then if on c_str
it is not known to be null terminated, we use a passed in buffer to copy
the string and ensure null termination.
This is a breaking change to dependencies that use the static ntcore
library. Unless the wpiutil library is also linked, linker errors will
result. This does not affect the shared ntcore library.
