Opt tests

Adds tests for optAUC functions and optRMSE functions. Changes safeOptAUC and greedOptAUC to issue a warning and a message respectively in case of optimization underperforming a component model. In the case of safeOptAUC, the best model is weighted 1 and returned, in greedOptAUC the best optimization is returned with a message. 

Basic tests for greedOptRMSE and ability to issue a message in degenerate cases. However, no tests for degenerate cases are included because I couldn't generate any data to do this. 

Closes #75. 
It actually dates back to [this answer on stackoverflow](http://stackoverflow.com/a/14948612/345660).  I think `colSums` might be faster than `colMeans` and yields the same model weights?