PuTTY 0.64 GSS-API keyex 1.0

Changes compared to upstream PuTTY 0.64:

• Support for GSS-API key exchange and gssapi-keyex authentication.
• Support for Heimdal GSS-API.
• 64-bit binaries and installer.
• Data Execution Prevention enabled for all binaries.
• Binaries and installer signed using Microsoft Authenticode.

Changes compared to PuTTY 0.63 GSS-API keyex 1.2:

• Update README.txt in binary distribution to describe GSS-API keyex specifics.
• Rebase to upstream PuTTY 0.64, which includes the following changes:
• Security fix: PuTTY no longer retains the private half of users' keys in memory by mistake after authenticating with them.
• Support for SSH connection sharing, so that multiple instances of PuTTY to the same host can share a single SSH connection instead of all having to log in independently.
• Command-line and configuration option to specify the expected host key(s).
• Defaults change: PuTTY now defaults to SSH-2 only, instead of its previous default of SSH-2 preferred.
• Local socket errors in port-forwarded connections are now recorded in the PuTTY Event Log.
• Bug fix: repeat key exchanges in the middle of an SSH session now never cause an annoying interactive host key prompt.
• Bug fix: reset the bolded-text default setting back to what it used to be. (0.63 set it to something wrong, as a side effect of refactoring.)
• Bug fix: IPv6 literals are handled sensibly throughout the suite, if you enclose them in square brackets to prevent the colons being mistaken for a :port suffix.
• Bug fix: IPv6 dynamic port forwardings should work again.