1. Modified vcf_parse to update rlen only when an END INFO tag is seen -

Issue: https://github.com/broadinstitute/gamgee/issues/191
1. Modified vcf_parse to update rlen only when an END INFO tag is seen -the END tag is NOT encoded into v->shared.s
2. Modified vcf_write to add END INFO tag if required

Yes, it is called only when writing a VCF file (not BCF). It can be used for debugging purposes by calling it directly (instead of through bcf_write or vcf_write).