Add "this commit" option to switch form

Branches are grouped into their own section to make the "this commit"
option visually distinct.

Adding this option will result in two options being marked as selected
if a branch has the same name as a commit oid.  But that would cause
all sorts of other problems anyway (attempting to switch to the branch
would actually give you the commit, etc.), so let's not worry about
that.

A "permalink" link on the blob view next to the "plain" link would
probably be more discoverable, but that would only work for the blob
view.  The switch UI is visible everywhere.

Signed-off-by: Alyssa Ross <hi@alyssa.is>

0 files changed, 0 insertions, 0 deletions