Warn the user about required PATH entry ordering

[petemounce]

As discovered within #1919, the order of entries in the PATH matters, and is hard to diagnose when it's wrong.

• add the warning message
• try it out on clean windows box
• ❓ mention this in the windows.md doc? It's a pretty inscrutable environment error, and I'd assume most people installing bazel on windows will already have git, so would be affected right out of the gate.
• bump the package version number according to chocolatey's package fix version notation

Once I've done both of those, I'll publish the package after this has been merged.

[bazel-io]

Can one of the admins verify this patch?

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[petemounce]

I signed it!

[dslomov]

This is good, although it would be even more awesome if we actually detected the failuer condition and warned user (if user axtually has msys-2.0.dll in path that is not from c:\tools\msys2\usr\bin or bash.exe that is from c:\windows\ (not asking to do that in this PR, just a general idea)

[dslomov]

20160205 should be fine no?

[petemounce]

It should be, but has not been published to the feed.

[petemounce]

re: more awesome; yes, definitely. Thought about it. But it would require knowing and maintaining a list of apps that vendor msys2 I think? Or is there a way to detect that from PowerShell, before the zip is fetched and installed? Same for bash.exe. That also discounts manual installs of same.

[dslomov]

I was thinking just check the output of where msys-2.0.dll and yell at user if it is not in c:\tools\msys64\usr\bin. Ditto for where bash.exe (yell if it is in c:\windows\ because the it is definitely from u-o-w. Maybe not yell very loudly since it might still be ok.

[petemounce]

I updated the docs via #1938.

[abergmeier-dsfishlabs]

@dslomov Given the amount of time that multiple people now wasted and wasting with this - please check the found msys-2.0.dll for version or ABI compat.