Check that git-stripspace supports "--comment-lines"

It seems that versions of Git older than 1.8.2 are still in use in the
wild, so check that the installed version of Git supports the features
we need.  This avoids exposing the user to a confusing error message
when the Git version is too old.

Signed-off-by: John Keeping <john@keeping.me.uk>
bashcomplete: move option completion after command inspection

This will let us change how arguments are completed based on earlier
options.

Signed-off-by: John Keeping <john@keeping.me.uk>
bashcomplete: remove prefix from completed refs

This lets tab completion work properly when a prefix is in operation
that changes the namespace to be used for refs in the integration
branch.

Signed-off-by: John Keeping <john@keeping.me.uk>
Merge branch 'bashcomplete-prefix'

Improve bash completion when a prefix is being applied to refs.

* bashcomplete-prefix:
  bashcomplete: remove prefix from completed refs
  bashcomplete: move option completion after command inspection
Merge branch 'check-git-version'

Avoid displaying a cryptic error message when the installed Git version
is too old and so does not support the --comment-lines option to
git-stripspace.

* check-git-version:
  Check that git-stripspace supports "--comment-lines"