plumbing to give ReporterTask access to standard error.

I'll need this in a later diff.  We prefer to write to the same
standard error file handle, so things are easier to test.
evaluateOptions in Options+Testing should open and close reporters.

Added some asserts to verify that we never publish events without first
opening the reporter task.
show error when reporter processes die prematurely.

xctool would previously exit and tell you nothing.  Now we'll show...

```
ERROR: Reporter 'test.sh' exited prematurely with status (0).
```
fixing the places that had MACOSX_DEPLOYMENT_TARGET = 10.8

We want to go 10.7 for as long as we can.