Because it now handles EINTR. And we should do so. While most people
use Linux, which tries very hard to avoid propagating EINTR back up
into userspace, it can still happen.
https://bugzilla.gnome.org/show_bug.cgi?id=682833
When interfacing with APIs that expect unix-style async I/O, it is
useful to be able to tell in advance whether a read/write is going to
block. This adds new interfaces GPollableInputStream and
GPollableOutputStream that can be implemented by a GInputStream or
GOutputStream to add _is_readable/_is_writable, _create_source, and
_read_nonblocking/_write_nonblocking methods.
Also, implement for GUnixInput/OutputStream and
GSocketInput/OutputStream
https://bugzilla.gnome.org/show_bug.cgi?id=634241