Avoid calling hal2fasta more than once when getting leaf blocks
Avoid calling hal2fasta more than once when getting leaf blocks

The old way of doing things was pretty slow on highly fragmented assemblies.

glennhickey/hal,glennhickey/hal,glennhickey/hal,glennhickey/hal,glennhickey/hal,glennhickey/hal,glennhickey/hal,glennhickey/hal