Additional error summary

I added some summary info to the log.  If there are no detected errors, nothing is logged.  However, in the case of compiler, syntax, or type errors, some additional stuff is shown.  I made it so the double chevron shows as red or green based on the presence of only non-emit-preventing type warnings.

![grunt-ts error reporting](https://cloud.githubusercontent.com/assets/3755379/3560461/9bb73498-096e-11e4-8547-5213e5753075.png)

I think that this could be further improved by summarizing type warnings per file.  If it seems a bit silly that there might ever be 172 type errors across multiple files, this is actually very plausible if you've either just implemented TypeScript from plain JS or else if you've just turned on no implicit any.

Please let me know what you think.

Note: the ts:fail task is failing when I build this.  I'm assuming that's ok?