Slice the 1-bp segment correctly within halCoverage
Slice the 1-bp segment correctly within halCoverage

toSite() already returns a 1-bp sliced segment. And funnily enough,
the code to slice a segment to 1-bp, if given to a segment *already*
sliced to 1-bp, happens to give back the full segment. This caused
halCoverage reports to be incorrect.

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