ctx.actions.write generates executable files even when asked not to

Code:
https://gist.github.com/endobson/1fa9fe0ad27eeaa8296c17187165d642
```
ctx.file_action(ctx.outputs.object, "object", False)
```

Output:
```
endobson@yggdrasil () ~/tmp/bazel-bug4 % ls -l bazel-bin/demo_rule.o
-r-xr-xr-x 1 endobson wheel 6 Apr 25 10:03 bazel-bin/demo_rule.o
```

Using self built release 0.4.5:
Build label: 0.4.5- (@non-git)
Build target: bazel-out/local-opt/bin/src/main/java/com/google/devtools/build/lib/bazel/BazelServer_deploy.jar
Build time: Tue Apr 25 06:47:27 2017 (1493102847)
Build timestamp: 1493102847
Build timestamp as int: 1493102847