CLI frontend: don't repeat plugin loading errors
CLI frontend: don't repeat plugin loading errors

And print them incrementally.

HadoopGenomics/Hadoop-BAM,HadoopGenomics/Hadoop-BAM,fnothaft/Hadoop-BAM,tomwhite/Hadoop-BAM,ryan-williams/Hadoop-BAM,cmnbroad/Hadoop-BAM,ryan-williams/Hadoop-BAM,tkrishp/Hadoop-BAM,fnothaft/Hadoop-BAM,HadoopGenomics/Hadoop-BAM,cmnbroad/Hadoop-BAM,fnothaft/Hadoop-BAM