sspi: print out InitializeSecurityContext() error message

Reported-by: Carsten (talksinmath)

Fixes #1384
Closes #1395

checksrc: white space edits to comply to stricter checksrc

vauth: Added check for supported SSPI based authentication mechanisms

Completing commit 00417fd66c and 2708d4259b.

spnego_sspi: fix memory leak in case *outlen is zero (#970)

vauth: Introduced Curl_auth_is_<mechansism>_supported() functions

As Windows SSPI authentication calls fail when a particular mechanism
isn't available, introduced these functions for DI

vauth: Introduced Curl_auth_is_<mechansism>_supported() functions

As Windows SSPI authentication calls fail when a particular mechanism
isn't available, introduced these functions for DIGEST, NTLM, Kerberos 5
and Negotiate to allow both HTTP and SASL authentication the opportunity
to query support for a supported mechanism before selecting it.

For now each function returns TRUE to maintain compatability with the
existing code when called.

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spnego: Corrected miss-placed * in Curl_auth_spnego_cleanup() declaration

Typo introduced in commit ad5e9bfd5d.

internals: rename the SessionHandle struct to Curl_easy

URLs: change http to https in many places

Closes #754

vauth: Corrected a number of typos in comments

Reported-by: Michael Osipov

vauth: Removed the need for a separate GSS-API based SPN function

spnego: Small code tidy up

* Prefer dereference of string pointer rather than strlen()
* Free challenge pointer in one place
* Additional comments

spnego: Renamed the context's SPN variable

To be consistent with the Kerberos 5 context and other authentication
code.

spnego: Corrected some typos in comments

Corrected typos from commit ad5e9bfd5d and 6d6f9ca1d9.

vauth: Moved the Negotiate authentication code to the new vauth directory

Part 2 of 2 - Moved the GSS-API based Negotiate authentication code.

vauth: Moved the Negotiate authentication code to the new vauth directory

Part 1 of 2 - Moved the SSPI based Negotiate authentication code.