Merge topic branch t/misc into pu

The stuff in here is too small to get its own topic branch. The
commits are generally regarded as safe enough to be applied directly to
"master" without cooking in "next" first. However, if a commit induces
a merge conflict or is important enough to get mentioned in an item
of the NEWS file, the commit should get a dedicated topic branch.

Unlike most other topic branches, this branch never promotes to
"next". When a set of commits is ready to graduate to "master", the
branch is rebased onto "master" and its commits are re-ordered so that
the graduating commits appear at the beginning. The last such commit
is merged to "master". This always results in a fast-forward merge,
so no merge message needs to be supplied.

* refs/heads/t/misc:
  gui: Kill also child processes of external commands.