Specified stream_user_data_arg can be retrieved by
spdylay_session_get_stream_user_data() function. The application code can use
this function insde spdylay_on_ctrl_send_callback() and identify stream ID
for the request associated by the stream_user_data.
The sample usage is in examples/spdycat.cc.

Conflicts:
	examples/spdylay_ssl.cc
	tests/Makefile.am
	tests/main.c

Changes:
        spdylay_select_next_protocol() returns -1 if it fails.
        Use cunit without pkg-config because debian does not provide .pc file.
        Some doc updates to suite my taste.
        Added spdylay_npn.h

Closes all server-pushed streams when original stream is closed by RST_STREAM with CANCEL from client.

Fixed spdylay_session_is_my_stream_id()

With this function and 3 new member in spdylay_stream, we can track server-
pushed streams which associate them to this stream.

We still does not check "url" is in nv.

Minor updates to make git status work better

SETTINGS ID is little endian in wire format despite the fact that spec/2 says it is network byte order.

Include sys/types.h for ssize_t

Now -nvh option works.

This is because our priority queue implementation does not have stable sort
property, so queueing SYN_STREAM, DATA in this order does not necessarily
mean SYN_STREAM will be sent first.