Add support for *clip.exe* for Bash on Ubuntu on Windows

[Jason A. Donenfeld]

On Tue, Jul 25, 2017 at 4:00 PM, Kenny Evitt <kenny.evitt at gmail.com> wrote:
> I just looked at this briefly and I've run into a couple of problems:
>
>  1. `uname` in Bash on Ubuntu on Windows (BUW) outputs `Linux`, so I'd have
> to name the platform file *linux.sh* or change the code in
> *password-store.sh* that sources those files.

Can you send me the output of this on WSL:

for i in a s n r v m p i o; do echo -n "uname -$i: "; uname -$i; done

>  2. `clip.exe` is unidirectional, i.e. there's no way for it to output the
> contents of the clipboard; nor is there a standard program for doing that
> either.
>
> Thoughts? Feelings?
>
> The Windows clipboard *can* be accessed from BUW via PowerShell – are you
> open to that as a dependency on Windows?

I don't want to introduce extra dependencies that aren't already
included with Windows or with WSL, but if there's some disgusting way
of shoving everything we need into the platform file, that'd be okay
with me.