os: remove trailing slash from os.tmpdir()

[tellnes]

This commit makes os.tmpdir() behave consistently on all platforms. It
changes os.tmpdir() to always return a path without trailing slash.

Semver: Major
Fixes: #715

[xaka]

1. What about more that one trailing slash if someone is messing up with env variables?
2. What about using path.normalize to take care of all possible scenarios?

[tellnes]

1. Can be easily fixed by s/if/while.
2. path.normalize does not remove trailing slashes.

[tellnes]

Maybe this:

path = require('path').normalize(path);
if (/[\\\/]$/.test(path))
  path = path.substr(0, path.length - 1);

(And of course putting the require call outside the function)

[bnoordhuis]

Suggestion: path = path.slice(0, -1);

[xaka]

One very important thing to think about. While __dirname isn't affected by user, os.tempdir() is, because it depends on env variable. Now imagine situation when user sets it wrong, io.js "fixes" it implicitly and it helps your program A to run, but at the same time another program B, written in another language, fails and you have no clue what's going on and why something works and something doesn't. What if program B depends on results of program A, both sharing the same env variables, but as program B doesn't know how to fix trailing slash, it's going to crash. I see how DevOps life might get in trouble here. Probably it's not a big deal, but who knows.

[rvagg]

collaborators: please hold off on merging this even if you think it's a good idea, a semver-major change is kind of a big deal at this stage still.

[bnoordhuis]

LGTM with a suggestion and no strong opinion on using path.normalize().

@tellnes Can you land it on the 'next' branch?

[tellnes]

I'm getting some errors in test/sequential/test-fs-watch.js, so I'll wait on landing this untill I have investigated those.

[tellnes]

I can't reproduce the errors, so it was probably something flaky.

Landed in bb97b70