WiX support for building with VS 2012

The merge modules need to reference VC110 paths.
Use a variable for VC100 versus VC110 so that we don't copy a lot
of boilerplate around.

ticket: 7666 (new)
queue: kfw
tags: pullup
target_version: 1.11.4
Require Windows Installer 4.5 or higher

As advised by the VC 11 merge modules.

Windows Installer 4.5 requires Windows Server 2008, Windows Vista, Windows XP
with Service Pack 2 (SP2) and later, or Windows Server 2003 with Service
Pack 1 (SP1) and later.  I believe we already enforce these restrictions
manually elsewhere, so this should not restrict our set of valid target
machines.

ticket: 7667 (new)
queue: kfw
tags: pullup
target_version: 1.11.4
Update windows README for VS2012/Windows SDK 8

The Windows SDK 8 dropped the command-line build environment, so
provide instructions for building with the Visual Studio (2012)
command-line build environment.

ticket: 7669 (new)
queue: kfw
tags: pullup
target_version: 1.11.4