test: restat handles depfile dependencies properly

Test for https://github.com/martine/ninja/issues/144
Tested to fail with https://github.com/maximuska/ninja/commit/123d3773cb23a9fa51573aa5eb74a00735e0203e applied.

I had to enhance FakeCommandRunner::StartCommand() to write a depfile to test this.

I will add a test for this use-case with deps=gcc later