Makefile: keep node/src, build test-list first, test wiki.

When saving node/src during build, cp rather than mv. That way the
working set is ok if git checkout aborts.
Build test/test-list first so test/runner.html works even if the build fails.
Add wiki as test dependency, so 'make test' builds everything.

TBR=johnjbarton

Review URL: https://github.com/google/traceur-compiler/pull/603

Closes #603.