fix coverage calculation issue

[yunfeiguo]

total length (defined by /home/yunfeiguo/projects/PacBio_reference_genome/novel_seq/novel_seq_characeterization_20160519/nohg38/novel_seq_index/hx1f4full3rdfixedv2.nohg38full+decoy.cov90idt90.10kb.absCoord.bed.fasta.bed) = 12.85Mb
Fraction of reads mapped to target region = 100.00%
Average coverage in target region = 3.13
Percentage above 30=0.46%
Percentage above 20=0.53%
Percentage above 10=0.77%
Percentage above 5=1.29%

Actually here, seqmule should also take unmapped reads into consideration.