[krbdev.mit.edu #6038] Add VS 2005 and VS 2008 support for the NSIS installer

[asanka@mit.edu via RT]

The attached patch modifies bkw.pl to invoke buildruntime.cmd to build
the runtime installer MSI for Visual Studio 2005 and 2008.  The
buildruntime.cmd script attempts to determine the current compiler using
the MSVCVer environment variable, which isn't a reliable way to detect
the version of the compiler that was used to build the rest of Kerberos
for Windows.

Ideally, the compiler version should be determined by the build system
and used to pull in the correct runtime libraries when building the
installers.

The patch is against the SVN trunk at /src/windows/build