Highlight foreground of selected line numbers

Previously no gutter highlight was displayed unless
the selection was empty.

Now there is a separate CSS class for no selection
that changes the background color independently
from the foreground color.

spec/stdlib/child-process-spec.coffee

@@ -126,4 +126,4 @@ describe 'Child Processes', ->
           ChildProcess.exec(cmd, options)
 
         runs ->
-          expect(output.length).toBeGreaterThan 1
+          expect(output.length).toBeGreaterThan 1