Use CWD for temp files, and fall back to /tmp only for upstream tests.
Use CWD for temp files, and fall back to /tmp only for upstream tests.

gopherjs/gopherjs,gopherjs/gopherjs,gopherjs/gopherjs,jargv/gopherjs,jargv/gopherjs,bpowers/gopherjs,gopherjs/gopherjs,albrow/gopherjs,bpowers/gopherjs,jargv/gopherjs,albrow/gopherjs,gopherjs/gopherjs,albrow/gopherjs,bpowers/gopherjs