Document `--sam-no-qname-trunc`

[BenLangmead]

The --sam-no-qname-trunc parameter instructs Bowtie 2 to print the complete read name to the SAM file even if it contains whitespace. This violates the SAM spec, but is often desirable in pipelines that use Bowtie 2 as a subcomponent. (Such pipelines usually "fix" the malformed SAM before ultimately reporting it.) It's been in Bowtie 2 for a while, but never documented. I vote we document it. This should include adding text to the manual under "SAM output" -> "1. Name of read that aligned" noting that the standard behavior of truncating at the first whitespace can be suppressed with --sam-no-qname-trunc, at the expense of generating non-standard SAM.