First pass at a transparent wrapper to run native cmake from cygwin.
Fixes to cmake-mswin.bash.

cmake-mswin.bash was failing intermittently. I'm not sure what the problem
is, but it typically comes up when we pass a param that has a space in it.
The path to cmake would no longer stay in quotes and cmd would complain about
"C:\Program" not being an executable file.

I've examined the params we were passing over to cmd.exe. They are always
correct and quoted properly. This is likely a cygwin/cmd interaction issue.

The workaround is, rather than calling the full path to cmake, adding the
path to cmake to PATH, then calling just cmake.
Changed an error message.

We used to have to start cl builds from some child process that was
started in the developer prompt. We can now source those vars directly.
All that remains is locating CMAKE, and that's what the error describes
now.
Mswin now -almost- builds.