Update kfw installer for VS2017, WiX 3.11.1

For Visual Studio 2017 (aka 15.0), add a Visual C tools version
number, and use %VCToolsRedistDir% to find the merge modules.  WiX
toolset 3.11.1 requires an xmlns attribute to the WixLocalization tag.

https://github.com/krb5/krb5/commit/ebaa5985234d6d331d1a3896fc485a798fa182a6
Author: Greg Hudson <ghudson@mit.edu>
Commit: ebaa5985234d6d331d1a3896fc485a798fa182a6
Branch: master
 src/windows/installer/wix/config.wxi            |    2 +
 src/windows/installer/wix/files.wxi             |   46 ++++++++++++----------
 src/windows/installer/wix/lang/strings_1033.wxl |    4 +-
 3 files changed, 29 insertions(+), 23 deletions(-)