add IOUtil.unrollFiles(INPUT, IOUtil.VCF_EXTENSIONS); to MergeVcfs (#729)
add IOUtil.unrollFiles(INPUT, IOUtil.VCF_EXTENSIONS); to MergeVcfs (#729)

* add IOUtil.unrollFiles(INPUT, IOUtil.VCF_EXTENSIONS); to MergeVcfs

* answer to https://github.com/broadinstitute/picard/pull/729#pullrequestreview-16581170

broadinstitute/picard,broadinstitute/picard,alecw/picard,alecw/picard,annkupi/picard,alecw/picard,alecw/picard,broadinstitute/picard,broadinstitute/picard,nh13/picard,annkupi/picard,annkupi/picard,annkupi/picard,broadinstitute/picard,nh13/picard,nh13/picard,nh13/picard