Previously, when we send all given buffer in data_source_callback, we
return NGHTTP2_ERR_DEFERRED, and nghttp2 library removes this stream
temporarily for writing.  This itself is good.  If this is the sole
stream in the session, nghttp2_session_want_write() returns zero,
which means that libcurl does not check writeability of the underlying
socket.  This leads to very slow upload, because it seems curl only
upload 16k something per 1 second.  To fix this, if we still have data
to send, call nghttp2_session_resume_data after nghttp2_session_send.
This makes nghttp2_session_want_write() returns nonzero (if connection
window still opens), and as a result, socket writeability is checked,
and upload speed becomes normal.

Stop curl from failing when non-fatal alert is received during
handshake.  This e.g. fixes lots of problems when working with https
sites through proxies.

Reported-by: bsammon
Bug: https://github.com/bagder/curl/issues/282

.. also correct some variable naming in curl_easy_escape.3

Bug: https://github.com/bagder/curl/issues/281


Reported-by:  <bsammon@users.noreply.github.com>

BoringSSL removed support for direct callers of SSL_CTX_callback_ctrl
and SSL_CTX_ctrl, so move to a way that should work on BoringSSL and
OpenSSL.

re #275

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!