build.txt: WiX 3.9 is out.

git-svn-id: http://tortoisesvn.googlecode.com/svn/trunk@26039 4cfb86a4-2c7a-11df-bd14-c1e331e6ceac
Update WiX location in default.build.user.tmpl too.

git-svn-id: http://tortoisesvn.googlecode.com/svn/trunk@26040 4cfb86a4-2c7a-11df-bd14-c1e331e6ceac
Always accept all failures if the user choses to ignore the warnings.

git-svn-id: http://tortoisesvn.googlecode.com/svn/trunk@26041 4cfb86a4-2c7a-11df-bd14-c1e331e6ceac