Function Sam-Header-Ensure-Hd

Part of:

package elprep
( sam-header-ensure-hd < hdr > &key (vn *sam-file-format-version*) < so > < go > )
Ensure an @HD line is present in the given sam-header.
See http://samtools.github.io/hts-specs/SAMv1.pdf - Section 1.3, Tag @HD.