Support for -culling_limit

[nathanweeks]

The -culling_limit option is occasionally useful for filtering, and can reduce run time as well. It would be helpful if this were supported by Galaxy BLAST+.

[peterjc]

If you want to work on a pull request, that'd be great.

It looks like it can't be combined with -best_hit_overhang or -best_hit_score_edge, which would complicate trying to offer those as well and enforcing this in the Galaxy GUI. But if you think the culling limit is more useful, we could prioritise adding that?

[nathanweeks]

I can look into submitting a pull request---hopefully before someone wants -best_hit_overhang or -best_hit_score_edge! I'll hold off on starting this until galaxy_blast incorporates BLAST 2.7.1+, which fixes a -culling_limit bug I had reported to NCBI.

[peterjc]

Cross reference #93