Move onto shell-qq.
Also change egid.
Fix bug in exception handling logic in Execute.

We should uncheck running/sudoing statuses on exceptions happening while
processing term operations.

That bug actually happens without sudoing too, but it does not matter
there because nobody checks running/sudoing statuses when not sudoing.
shell primitive does not provide any value in the presence of sh quasiquoter.
shell-qq -> command-qq.
Add Mip.
Reworked sudoing algorithm.
Document algorithm.
Cosmetics.
Get back to initial uid/gid after all tasks are scheduled.
Haddock fixes.
Merge branch 'feature-command-qq' into develop