Focus on mouseup instead of mousedown

Focus the terminal on mouseup if the button is not the right mouse
button. In addition, do not focus if there is text selected to prevent
the selection from disappearing.

lib/view.coffee

@@ -64,9 +64,11 @@ class TerminalPlusView extends View
       event.preventDefault()
       event.stopPropagation()
 
-    @xterm.on 'mousedown', (event) =>
+    @xterm.on 'mouseup', (event) =>
       if event.which != 3
-        @focus()
+        text = window.getSelection().toString()
+        unless text
+          @focus()
     @xterm.on 'dragenter', override
     @xterm.on 'dragover', override
     @xterm.on 'drop', @recieveItemOrFile