Some support for VCF v4.2 files added:
Handles "Number=R" for INFO fileds in the header.
Other VCF v4.2 specific additions (Eg: Source and Version fields in INFO header lines) are not handled, but appear to be silently ignored.
Tested on output of samtools mpileup | bcftools call (1.0-17-gfaf4dd6, 1.0-55-gc661821, using htslib 1.0-11-g830ea73)