Turn install.bat into a pure one line wrapper fort he perl script.

Turn install.bat into a pure one line wrapper fort he perl script.

Build.bat and vcregress.bat got similar treatment years ago. I'm not sure
why install.bat wasn't treated at the same time, but it seems like a good
idea anyway.

The immediate problem with the old install.bat was that it had quoting
issues, and wouldn't work if the target directory's name contained spaces.
This fixes that problem.

I committed this to master yesterday, this is a backpatch of the same for
all supported versions.