Ignore first modified event in config editor

This event comes from initially setting the text for the current
config value on the editor and was causing the config to be
immediately saved multiple times when opened.

spec/app/config-panel-spec.coffee

@@ -67,6 +67,7 @@ describe "ConfigPanel", ->
     config.set('foo.float', 1.1)
     config.set('foo.string', 'I think therefore I am.')
     panel = new TestPanel
+    window.advanceClock(10000) # wait for contents-modified to be triggered
     expect(panel.intEditor.getText()).toBe '1'
     expect(panel.floatEditor.getText()).toBe '1.1'
     expect(panel.stringEditor.getText()).toBe 'I think therefore I am.'
@@ -100,3 +101,15 @@ describe "ConfigPanel", ->
     expect(config.get('foo.int')).toBe undefined
     expect(config.get('foo.float')).toBe undefined
     expect(config.get('foo.string')).toBe undefined
+
+  it "does not save the config value until it has been changed to a new value", ->
+    class TestPanel extends ConfigPanel
+      @content: ->
+        @div =>
+          @subview "foo.int", new Editor(mini: true, attributes: {id: 'foo.int', type: 'int'})
+
+    config.set('foo.int', 1)
+    spyOn(config, 'set')
+    new TestPanel
+    window.advanceClock(10000) # wait for contents-modified to be triggered
+    expect(config.set).not.toHaveBeenCalled()

src/app/config-panel.coffee

@@ -48,5 +48,6 @@ class ConfigPanel extends View
           value ?= ""
           editor.setText(value.toString())
 
-        editor.getBuffer().on 'contents-modified', =>
-          config.set(name, @parseValue(type, editor.getText()))
+        editor.getBuffer().one 'contents-modified', =>
+          editor.getBuffer().on 'contents-modified', =>
+            config.set(name, @parseValue(type, editor.getText()))