Run conditional reciprocal best blast

 CRB-BLAST is a novel method for finding orthologs between one set of sequences
 and another. This is particularly useful in genome and transcriptome
 annotation.
 .
 CRB-BLAST initially performs a standard reciprocal best BLAST. It does this by
 performing BLAST alignments of query->target and target->query. Reciprocal
 best BLAST hits are those where the best match for any given query sequence in
 the query->target alignment is also the best hit of the match in the reverse
 (target->query) alignment.
 .
 Reciprocal best BLAST is a very conservative way to assign orthologs. The main
 innovation in CRB-BLAST is to learn an appropriate e-value cutoff to apply to
 each pairwise alignment by taking into account the overall relatedness of the
 two datasets being compared. This is done by fitting a function to the
 distribution of alignment e-values over sequence lengths. The function
 provides the e-value cutoff for a sequence of given length.