Closes #565

Make this the default for the curl tool (if built with HTTP/2 powers
enabled) unless a specific HTTP version is requested on the command
line.

This should allow more users to get HTTP/2 powers without having to
change anything.

... and stick to 1.1 for HTTP. This is in line with what browsers do and
should have very little risk.

Closes #491

Closes #555

Reported-by: Thomas Klausner

When NGHTTP2_ERR_PAUSE is returned from data_source_read_callback, we
might not process DATA frame fully.  Calling nghttp2_session_mem_recv()
again will continue to process DATA frame, but if there is no incoming
frames, then we have to call it again with 0-length data.  Without this,
on_stream_close callback will not be called, and stream could be hanged.

Bug: http://curl.haxx.se/mail/lib-2015-11/0103.html
Reported-by: Francisco Moraes

With curl disable verbose strings in http.c the compilation fails due to
the data variable being undefined later on in the function.

Closes #558

The name of the header guard in lwIP's <lwip/opt.h> has changed from
'__LWIP_OPT_H__' to 'LWIP_HDR_OPT_H' (bug #35874 in May 2015).

Other fixes:

- In curl_setup.h, the problem with an old PSDK doesn't apply if lwIP is
used.

- In memdebug.h, the 'socket' should be undefined first due to lwIP's
lwip_socket() macro.

- In curl_addrinfo.c lwIP's getaddrinfo() + freeaddrinfo() macros need
special handling because they were undef'ed in memdebug.h.

- In select.c we can't use preprocessor conditionals inside select if
MSVC and select is a macro, as it is with lwIP.

http://curl.haxx.se/mail/lib-2015-12/0023.html
http://curl.haxx.se/mail/lib-2015-12/0024.html

- If the size of the length type (curl_off_t) is greater than the size
of the size_t type then check before allocating memory to make sure the
value of length will fit in a size_t without overflow. If it doesn't
then return CURLE_BAD_FUNCTION_ARGUMENT.

Bug: https://github.com/bagder/curl/issues/425#issuecomment-154518679
Reported-by: Steve Holme

They didn't match the ifdef logic used within libcurl anyway so they
could indeed warn for the wrong case - plus the tool cannot know how the
lib actually performs at that level.

Tests 842, 843, 844, 845, 887, 888, 889, 890, 946, 947, 948 and 949 fail
if a custom port number is specified via the -b option of runtests.pl.

Suggested by: Kamil Dudka
Bug: http://curl.haxx.se/mail/lib-2015-12/0003.html

for all we know now, it might be called 7.46.1

Closes #546

- set the correct stream_id for pushed streams
- init maxdownload and size properly

give the new stream the old one's stream_weight internally to avoid
sending a PRIORITY frame unless asked for it

Fixes warnings 78c25c85 added.

IoctlSocket() apparently wants a pointer to a long, passed as a char *
in its third parameter. This bug was introduced already back in commit
c5fdeef4 from October 1 2001!

Bug: http://curl.haxx.se/mail/lib-2015-11/0088.html
Reported-by: Norbert Kett

Reported-by: Mohammad AlSaleh