This writes some pretty gnarly messages into the console:

```
info: r2d2b2g: executing 'r2d2b2g/tests/test-validator.test permission access on permission without access'
error: r2d2b2g: An exception occurred.
Error: PermissionsTable.jsm: expandPermissions: Invalid Manifest : alarms readonly

resource://gre/modules/PermissionsTable.jsm 323
Traceback (most recent call last):
  File "resource://gre/modules/commonjs/sdk/timers.js", line 31, in notify
    callback.apply(null, args);
  File "resource://gre/modules/commonjs/sdk/deprecated/unit-test.js", line 288, in 
    timer.setTimeout(function() { onDone(self); }, 0);
  File "resource://gre/modules/commonjs/sdk/deprecated/unit-test.js", line 458, in 
    options.onDone(self);
  File "resource://gre/modules/commonjs/sdk/deprecated/unit-test.js", line 440, in runNextTest
    self.start({test: test, onDone: runNextTest});
  File "resource://gre/modules/commonjs/sdk/deprecated/unit-test.js", line 471, in start
    this.test.testFunction(this);
  File "resource://gre/modules/commonjs/sdk/test.js", line 72, in 
    test(assert);
  File "resource://r2d2b2g-at-mozilla-dot-org/r2d2b2g/tests/test-validator.js", line 244, in exports["test permission access on permission without access"]
    validator.validatePermissions(errors, warnings, manifest, app);
  File "resource://r2d2b2g-at-mozilla-dot-org/r2d2b2g/lib/validator.js", line 185, in 
    permissionsNames.forEach(function(name) {
  File "resource://r2d2b2g-at-mozilla-dot-org/r2d2b2g/lib/validator.js", line 197, in 
    if (access && expandPermissions(name, access).length === 0) {
  File "resource://gre/modules/PermissionsTable.jsm", line 323, in expandPermissions
    throw new Error(errorMsg);
```

I think we'd be better off calling *console.error* or even just *console.warn* to write a simple one-line message like `Error: PermissionsTable.jsm: expandPermissions: Invalid Manifest : alarms readonly`, since the stack isn't significant to users, nor do we particularly benefit from it.