Pick-your-own columns tabular output for BLAST+ tools.

Note this moves the $out_format parameter inside a conditional block.

Currently this only offers the same 25 columns already available
via our extended tabular output - adding the rest is easy but the
best user interface needs a little thought...
More BLAST+ blastn test files
Test blastn XML and tabular pick-your-own column output
Be consistent about using NCBI's grammar
Column picking test for blastxml_to_tabular