Merge pull request #2830 from gustavobgama/fix/master/nfs_typo

Fix typo
core: don't use Tempdir for tests, use Dir.mktmpdir

Tempdir didn't work on Windows, just spun forever.
test: allow skipping certain tests on Windows
core: fix Windows failures on machine tests
core: fix tests failing on WIndows dueo to bad temp dir gen
core: fix more cases where ".path" was being called on strings
core: don't test fork(1) on Windows