Drop dependency on mercurial, not using it.
Switch prefix to toolshed and testtoolshed...

... instead of tsm and tst.
Rebuild repository from scratch each run.
Fix download_file when extract="true".

Last thing needed for whole emboss dependency tree.
Add brew option --without-architecture to force source only tool shed installs.

It is a vague approximation - like many of these conversions.
Remove stray print.