Add a test for CreatePhonyInEdge() in depsmode path.

Removing the `CreatePhonyInEdge(node);` line in
`ImplicitDepLoader::LoadDepsFromLog()` made no tests fail before this change.
The new test is a port to depsmode of the existing DepFileOK test.
Merge pull request #593 from nico/moretest

Add a test for CreatePhonyInEdge() in depsmode path.