VCS-76: Something hosed w git submodules handling

[m0j0hn]

I am trying to use Glide on Linux and Windows, and for one of my modules with submodules, it's failing on Windows. Some Googling revealed Glide issue #745, which referenced line 388 in git.go.
After manually trying the underlying git commands on my Windows, I think root cause is that "git submodule foreach ... --prefix=..." passes the prefix string as a doublequote delimited string to Windows bash, and the trailing '' (Windows PathDelimiter) escapes the closing doublequote, which Breaks Things (tm). My inelegant solution is to create helper function which is used to conditionally rewrite the path string on Windows by tripling every PathDelimiter, i.e., '' becomes '\' - and this seems to solve the problem. I also added another test using a publicly accessible repo which exercised the original problem which led me to work on this in the first place.

[m0j0hn]

@mattfarina @technosophos Can you please consider this Issue and the PR for its fix?
#77

[mattfarina]

I merged the PR. I'll update glide in the next couple days when I get a moment.