Fixing OnpCombiner for indels only files
  fixing an additional indel ordering issue
  added a warning for out of order files when running with --infer-onps
  running out of order may fail to combine some onps
  it may also lead to storing large numbers of mutations in memory while waiting to combine them
Merge pull request #278 from broadinstitute/lb_fix_indels_only_onp

Fixing OnpCombiner for indels only files