Fixed: sorting order lost during merge step of sort tool, if input BAM

lacked SAM header
 * Due to lack of SO tag in temp files. This tag is set just fine on
input BAMs containing SAM headers. However, when an input file lacked
one, especially the (required) VN number, the entire @HD line was
dropped.
 * Forcing the current SAM version number, if none exists, on sort
output.