Closes #361

The SSH state machine didn't clear the 'rc' variable appropriately in a
two places which prevented it from looping the way it should. And it
lacked an 'else' statement that made it possible to erroneously get
stuck in the SSH_AUTH_AGENT state.

Reported-by: Tim Stack

Closes #357

initialization discards 'const' qualifier from pointer target type

Closes #360

References to NTLM in the identity generation should have been removed
in commit c4699412 but not all were.

connect.c:953:5: warning: initializer element is not computable at load
                 time
connect.c:953:5: warning: missing initializer for field 'dwMinorVersion'
                 of 'OSVERSIONINFOEX'
curl_sspi.c:97:5: warning: initializer element is not computable at load
                  time
curl_sspi.c:97:5: warning: missing initializer for field 'szCSDVersion'
                  of 'OSVERSIONINFOEX'

schannel.c:1125:5: warning: missing initializer for field 'dwMinorVersion'
                   of 'OSVERSIONINFOEX' [-Wmissing-field-initializers

Bug: http://curl.haxx.se/mail/lib-2015-07/0149.html
Reported-by: Eric Ridge

Bug: http://curl.haxx.se/mail/lib-2015-07/0149.html
Reported-by: Eric Ridge

...as well as some rewording.

Otherwise it would never be called for an HTTP/2 connection, which has
its own disconnect handler.

I spotted this while debugging <https://bugzilla.redhat.com/1248389>
where the http_disconnect() handler was called on an FTP session handle
causing 'dnf' to crash.  conn->data->req.protop of type (struct FTP *)
was reinterpreted as type (struct HTTP *) which resulted in SIGSEGV in
Curl_add_buffer_free() after printing the "Connection cache is full,
closing the oldest one." message.

A previously working version of libcurl started to crash after it was
recompiled with the HTTP/2 support despite the HTTP/2 protocol was not
actually used.  This commit makes it work again although I suspect the
root cause (reinterpreting session handle data of incompatible protocol)
still has to be fixed.  Otherwise the same will happen when mixing FTP
and HTTP/2 connections and exceeding the connection cache limit.

Reported-by: Tomas Tomecek
Bug: https://bugzilla.redhat.com/1248389

and made the indent level to 1

... and some general rewordings to improve this docs.

Reported-by: Tim Stack

Closes #356

VC7, VC11, VC12 and VC14 makefiles were missing from the release
tarball.

Updates to Makefile.am for the generation of the project files in
the tarball to follow.

Whilst there are no coding standards for the batch files used in curl,
most tend to use lower-case for keywords and upper-case for variables.

Visual Studio project files and updates to makefile.am to follow.

This wasn't possible with the old curlsrc project filenames, but like
commit 2a615a2b and 11397eb6 for libcurl use the built in Visual
Studio macros for the output filenames.

Following commit 957fcd90 and in preparation for adding the VC14
project files renamed the curl source project files.

.. also update formatting and add WinSSL and wolfSSL to the SSL/TLS
handlers list.

This is a new document to consolidate our thread safety information from
several documents (curl-www:features, libcurl.3, libcurl-tutorial.3).
Each document's section on multi-threading will now point to this one.