xP: make middle click close buffers

As if they were tabs, to save pointless typing.

xP/public/xP.js

@@ -465,6 +465,14 @@ let BufferList = {
 			// The role makes it selectable in VIM-like browser extensions.
 			return m('.item[role=tab]', {
 				onclick: event => bufferActivate(name),
+				onauxclick: event => {
+					if (event.button == 1)
+						rpc.send({
+							command: 'BufferInput',
+							bufferName: name,
+							text: '/buffer close',
+						})
+				},
 				class: classes.join(' '),
 			}, displayName)
 		})