Add a [/] macro expansion for tests

[nipunn1313]

Converts to backslash on windows. Currently, we're using [..],
so this will tighten up the tests.

[rust-highfive]

r? @alexcrichton

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[alexcrichton]

Nice idea! Looks like there may still be a few instances of failures on AppVeyor?

[nipunn1313]

Looks like cargo read-manifest returns a string with multiple backslashes (like src\foo.rs) which doesn't match the src[/]foo.rs (previously matching src[..]foo.rs). Perhaps this is a bug in cargo read-manifest to output the double backslash? Or an odd intended behavior? For now, I reverted converting the read-manifest test.

[alexcrichton]

@bors: r+

Huh, odd!

[bors]

📌 Commit 2435936 has been approved by alexcrichton

[bors]

⌛ Testing commit 2435936 with merge 0682ced...

[bors]

☀️ Test successful - cargo-cross-linux, cargo-linux-32, cargo-linux-64, cargo-mac-32, cargo-mac-64, cargo-win-gnu-32, cargo-win-gnu-64, cargo-win-msvc-32, cargo-win-msvc-64
Approved by: alexcrichton
Pushing 0682ced to master...