Add Blast+ package. (#3562)

* Add Blast+ package.

Adds support for NCBI's blast+@2.6.0.  I'll be adding a few historical versions in the near future.

It's a fairly direct transliteration of the [Homebrew Science recipe][hbs].

I skipped the mysql support.

There is a problem with HDF5 support.  Blast's configure script test program defines a macro 'HOST' to a string value and one of the HDF5 bits has an variable named 'HOST'.  Fun things happen.   I've disabled support for now.

I've run very very basic tests.  I'll get this out to my users and ensure that it works and fine tune the options and etc....

[hbs]: https://github.com/Homebrew/homebrew-science/blob/master/blast.rb

* Flake8 fixes

* Update w.t.r. mamelara's PR and cleanup

Add paths to things in the --with-* config args

Add add'l config flags from #3394.

Update patch to no-op and add comment.

Add add'l dependencies after studying `configure --help`.

* Flake8 cleanup

* Add support for blast+@2.2.30

Need to work around a configure bug.  See https://github.com/Homebrew/homebrew-science/issues/2337#issuecomment-170011511.

* Re-wrap comment, line length not a problem.

I'd broken a comment across to line in a fit of flake8
induced fear.  Adam pointed out that it's ok.

* Remove explicit prefix config

Remove explicit prefix config, the autotools package does it for us.