swc-windows-installer.sh: Convert script from Python to POSIX shell

On Mon, Jan 13, 2014 at 05:49:51AM -0800, Aron Ahmadia wrote:
> We currently have an installer that handles the issue of installing
> `nano` into msysgit for use with Git: ...
>
> This currently doesn't help for bootcamps where Python is not
> installed, so it would be handy to have a version of this that
> doesn't rely on a Python install.

POSIX shell, because an interpreted language from 1977 [1] is more
widely supported than an interpreted language from 1991 [2].  It looks
like the default msysGit install sets up the right double-click magic
too:

On Mon, Jan 13, 2014 at 10:03:24AM -0800, Ethan White wrote:
> Will a POSIX version run by simply double clicking the file?

On Mon, Jan 13, 2014 at 10:25:33AM -0800, Ethan White wrote:
> Just checked this on my Windows machine and it actually seems to
> work automatically as long as GitBash is installed and the file has
> a .sh extension. So POSIX away.

[1]: http://en.wikipedia.org/wiki/Bourne_shell
[2]: http://en.wikipedia.org/wiki/Python_language
Merge branch 'master' into bc-namespaced

* master:
  swc-windows-installer.sh: Convert script from Python to POSIX shell