Error: CLANG_WARNING:
lib/http.c:173:16: warning: Value stored to 'http' during its initialization is never read

Error: COMPILER_WARNING:
lib/http.c: scope_hint: In function ‘http_disconnect’
lib/http.c:173:16: warning: unused variable ‘http’ [-Wunused-variable]

.. also make __func__ replacement in multi.

Prior to this change debug builds would fail to build if the compiler
was building pre-c99 and didn't support __func__.

Use a curl_off_t for upload left

as after 4883f701, the *_clean() function only flushes the hash.

As it breaks configure, curl-config and test 1023 if not.

.. and added unit1602 for hash.c

We could get stream ID not in the hash in on_stream_close.  For
example, if we decided to reject stream (e.g., PUSH_PROMISE), then we
don't create stream and store it in hash with its stream ID.

This commit requires nghttp2 v1.0.0 to compile, and migrate to v1.0.0,
and utilize recent version of nghttp2 to simplify the code,

First we use nghttp2_option_set_no_recv_client_magic function to
detect nghttp2 v1.0.0.  That function only exists since v1.0.0.

Since nghttp2 v0.7.5, nghttp2 ensures header field ordering, and
validates received header field.  If it found error, RST_STREAM with
PROTOCOL_ERROR is issued.  Since we require v1.0.0, we can utilize
this feature to simplify libcurl code.  This commit does this.

Migration from 0.7 series are done based on nghttp2 migration
document.  For libcurl, we removed the code sending first 24 bytes
client magic.  It is now done by nghttp2 library.
on_invalid_frame_recv callback signature changed, and is updated
accordingly.

... to "compartmentalize" a bit and make it easier to change behavior
when multiplexing is used instead of good old pipelining.

By setting this option to 1 libcurl will wait for a connection to reveal
if it is possible to pipeline/multiplex on before it continues.

... and suddenly things work much better!

... so that they'll get handled next in the multi loop.

to allow code to act differently on the situation.

Also added some more info message for the connection re-use function to
make it clearer when connections are not re-used.

It makes us use less memory when not doing HTTP/2 and subsequently also
makes us not have to cleanup HTTP/2 related data when not using HTTP/2!

Previously when we do pause because of out of buffer, we just throw
away unread data in connection buffer.  This just broke protocol
framing, and I saw occasional FRAME_SIZE_ERROR.  This commit fix this
issue by remembering how much data read, and in the next iteration, we
process remaining data.

This commit fixes the bug that streams get stuck if stream gets some
DATA, and stream->closed becomes true at the same time.  Previously,
in this condition, after we processed DATA, we are going to try to
read data from underlying transport, but there is no data, and gets
EAGAIN.  There was no code path to evaludate stream->closed.

... as it was only used from there.