External tasks support merged to the 0.16 development branch

[Nick Coghlan]

Dan merged the external task support to the development branch this
afternoon:
http://git.beaker-project.org/cgit/beaker/commit/?h=develop&id=07869a2c0...

The design proposal has also been updated based on the merged
implementation: http://beaker-project.org/dev/proposals/external-tasks.html

Note that the default beah harness is *not* compatible with the use of
fetch URLs - for the time being, this feature is designed to be used
solely with alternate harnesses (at least until we get restraint to a
state where we're happy with it replacing beah as the default harness).

Cheers,
Nick.