commit 6d5f40238028f2d8c (Apr 27) or later nghttp2 is now required

Carrying on from commit 11025613 added VC7 project files which are
capable of supporting side-by-side compilation, as well as support for
some of the third-party libraries curl uses.

Carrying on from commit 11025613 added a more thorough version of
the VC6 project files which are capable of supporting side-by-side
compilation, as well as support for some of the third-party libraries
curl uses.

set.infilesize in this case was modified in several places, which could
lead to repeated requests using the same handle to get unintendent/wrong
consequences based on what the previous request did!

... during the non-blocking SSL handshake

This makes the findprotocol() function work as intended so that libcurl
can properly be restricted to not support HTTP while still supporting
HTTPS - since the HTTPS handler previously set both the HTTP and HTTPS
bits in the protocol field.

This fixes --proto and --proto-redir for most SSL protocols.

This is done by adding a few new convenience defines that groups HTTP
and HTTPS, FTP and FTPS etc that should then be used when the code wants
to check for both protocols at once. PROTO_FAMILY_[protocol] style.

Bug: https://github.com/bagder/curl/pull/97
Reported-by: drizzt

Carrying on from commit 11025613 added VC12 project files which are
capable of supporting side-by-side compilation, 32-bit and 64-bit
builds as well as support for some of the third-party libraries curl
uses.

Versions since at least 2.9.4 renamed error.h to error-ssl.h, so use
whichever one is available.

gnutls_x509_crt_import() must not be called with a NULL certificate

Bug: http://curl.haxx.se/mail/lib-2014-04/0145.html
Reported-by: Damian Dixon

As this makes curl_global_init_mem() behave the same way as
curl_global_init() already does in that aspect - the same number of
curl_global_cleanup() calls is then required to again decrease the
counter and then eventually do the cleanup.

Bug: http://curl.haxx.se/bug/view.cgi?id=1362
Reported-by: Tristan

When --with-nghttp2 was used (without a given path), the
PKG_CONFIG_LIBDIR varialbe could get clobbered and ruin a proper
detection of the library.

Reported-by: Dilyan Palauzov
Bug: http://curl.haxx.se/mail/lib-2014-04/0159.html

copy and paste error

ufds might not be allocated in case nfds overflows to zero while
extra_nfds is still non-zero. udfs is then accessed within the
extra_nfds-based for loop.

Follow up on b0e74254