Add Plan 9 support

[fhs]

Fix build on Plan 9 and make all tests pass.

Note: running go test ./... may hang in TestTempFileMany or TestTempFileManyWithUtil. I'm not sure if it's a go tool issue, standard library issue, or something wrong with the tests. All tests pass if tests are run with go test -count 1 ./....

Fixes #52

Signed-off-by: Fazlul Shahriar [email protected]