Emit error when lintspaces fails. Clean-up for watch tasks.

I apologize for the lack of unit tests. I essentially had two problems when using this library and these changes scratched my itch.

- Using `gulp-lintspaces` in a watch would fail. If a file contained a whitespace error once, it would never be removed and be reported again on each change.
- The default reporter did not emit an error when lintspaces existed, making it difficult to exit with a non-zero exit code (used by CI to determine build success)