refFlat2bed.py: optionally merge overlapping exons with different gene names
coverage: err informatively if bedcov returns nothing

If sequence/contig/chromosome IDs don't match (e.g. chr1 vs. 1), bedcov happily
returns nothing at all, causing a divide-by-zero later. Catch this before it
confuses the user.
target: handle some more edge cases in split_targets
Merge branch 'master' of github.com:etal/cnvkit

Conflicts:
	cnvlib/target.py