Add pollable input/output streams

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

docs/reference/gio/gio-docs.xml

@@ -68,6 +68,8 @@
         <xi:include href="xml/gunixoutputstream.xml"/>
         <xi:include href="xml/gconverterinputstream.xml"/>
         <xi:include href="xml/gconverteroutputstream.xml"/>
+        <xi:include href="xml/gpollableinputstream.xml"/>
+        <xi:include href="xml/gpollableoutputstream.xml"/>
     </chapter>
     <chapter id="types">
         <title>File types and applications</title>

docs/reference/gio/gio-sections.txt

@@ -2934,3 +2934,44 @@ G_IS_PERIODIC
 <SUBSECTION Private>
 g_periodic_get_type
 </SECTION>
+
+<SECTION>
+<FILE>gpollableinputstream</FILE>
+<TITLE>GPollableInputStream</TITLE>
+GPollableInputStream
+GPollableInputStreamInterface
+<SUBSECTION>
+g_pollable_input_stream_can_poll
+g_pollable_input_stream_is_readable
+g_pollable_input_stream_create_source
+g_pollable_input_stream_read_nonblocking
+<SUBSECTION>
+GPollableSourceFunc
+g_pollable_source_new
+<SUBSECTION Standard>
+G_POLLABLE_INPUT_STREAM
+G_POLLABLE_INPUT_STREAM_GET_INTERFACE
+G_IS_POLLABLE_INPUT_STREAM
+G_TYPE_POLLABLE_INPUT_STREAM
+<SUBSECTION Private>
+g_pollable_input_stream_get_type
+</SECTION>
+
+<SECTION>
+<FILE>gpollableoutputstream</FILE>
+<TITLE>GPollableOutputStream</TITLE>
+GPollableOutputStream
+GPollableOutputStreamInterface
+<SUBSECTION>
+g_pollable_output_stream_can_poll
+g_pollable_output_stream_is_writable
+g_pollable_output_stream_create_source
+g_pollable_output_stream_write_nonblocking
+<SUBSECTION Standard>
+G_POLLABLE_OUTPUT_STREAM
+G_POLLABLE_OUTPUT_STREAM_GET_INTERFACE
+G_IS_POLLABLE_OUTPUT_STREAM
+G_TYPE_POLLABLE_OUTPUT_STREAM
+<SUBSECTION Private>
+g_pollable_output_stream_get_type
+</SECTION>

docs/reference/gio/gio.types

@@ -76,6 +76,9 @@ g_output_stream_splice_flags_get_type
 g_password_save_get_type
 g_periodic_get_type
 g_permission_get_type
+g_pollable_input_stream_get_type
+g_pollable_io_stream_get_type
+g_pollable_output_stream_get_type
 g_proxy_address_enumerator_get_type
 g_proxy_address_get_type
 g_proxy_get_type