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
PR-URL: #747
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>

This commit applies some secondary changes in order to make `make test`
pass cleanly:

* disable broken postmortem debugging in common.gypi

* drop obsolete strict mode test in parallel/test-repl

* drop obsolete test parallel/test-v8-features

PR-URL: #1232
Reviewed-By: Fedor Indutny <fedor@indutny.com>

Cherry-pick https://codereview.chromium.org/1033733003 from upstream
and re-enable postmortem debugging.

PR-URL: #1232
Reviewed-By: Fedor Indutny <fedor@indutny.com>

This includes the out-of-tree patch (but fixed in upstream HEAD) from
commit 41c00a2 ("deps: enable v8 postmortem debugging again".)

PR-URL: #1399
Reviewed-By: Fedor Indutny <fedor@indutny.com>

This commit applies a secondary change in order to make `make test`
pass cleanly, specifically re-disabling post-mortem debugging in
common.gypi.

Cherry-pick https://codereview.chromium.org/1033733003 from upstream
and re-enable postmortem debugging.

PR-URL: #1232
Reviewed-By: Fedor Indutny <fedor@indutny.com>