The ContinueTimer could expire before the full HEADERS frame was
actually sent. By moving the call to timer->start() to the
on_frame_send_callback(), this race is fixed.

If a 100 Continue interim response was received after the continue
timeout was reached, dispatch_continue() would force a double submission
of DATA frames. This patch prevents dispatch_continue() from doing
anything if the timer callback has already been invoked. This makes
ContinueTimer a single-shot mechanism, as originally intended.

To deal with servers that don't conform to RFC 7231 (or, potentially,
connections with a large round-trip time), don't wait forever for a 100
Continue status to come back. Currently, the timeout is hard-coded to
one second.

A ContinueTimer encapsulates the handshake timeout logic for a single
request. Somewhat counterintuitively, ContinueTimers are owned by the
HttpClient instead of the Request object, because their lifetime must be
bound to the life of the connection (which is owned by the HttpClient
and not the Requests). A Request is associated with its corresponding
ContinueTimer through a std::weak_ptr.

Requests that expect a 100 Continue will not submit their DATA frames
until the server sends the interim response.

Add a placeholder for the expect-continue option, which will perform an
Expect/Continue handshake for DATA uploads.

This reverts commit 6680d8b7.

It was added because the default RelWithDebInfo type disabled
assertions, but now that -DNDEBUG is removed from its flags, it is not
necessary to change the build type anymore.

failmalloc and main tests succesfully pass the test now.

Fix Windows build by defining `ssize_t` when missing and adjusting the
install commands.

Add support for ENABLE_WERROR=1 while at it.

Tested with MSVC 2013 on Windows 7 x64.

Avoid adding a LIBXML2_LIBRARIES-NOTFOUND to the libraries list when it
is not found. Likewise for OpenSSL.

Matches autotools behavior. The m4_if logic was misread...

Do not add _U_ and NGHTTP2_NORETURN definitions to the command line,
instead add it to config.h. This matches what autotools does.

Users can disable this by setting -DCMAKE_C_FLAGS=-DNDEBUG or
-DCMAKE_CXX_FLAGS=-DNDEBUG to disable assertions as desired.

src/Makefile.am: fix missing allocator.h

Build type-specific flags are added before other flags, reflect this in
the output.

NOTE: RelWithDebInfo *disables* assertions by default. To keep
assertions, use CMAKE_BUILD_TYPE=Debug or CMAKE_BUILD_TYPE=None.

Fix regression from v1.8.0-38-gbae37e3e breaking distcheck.

Add Nathan's PPA for cmake 3.2.3 (3.0 or newer is required).