Isolate folds on a per-display-buffer basis

Creating a fold in one pane now has no effect on an edit session
for the same buffer in another pane. Before they were polluting each
other by sharing the same fold markers.

spec/app/display-buffer-spec.coffee

@@ -257,6 +257,12 @@ describe "DisplayBuffer", ->
           expect(line0.fold).toBe outerFold
           expect(line1.fold).toBeUndefined()
 
+      describe "when there is another display buffer pointing to the same buffer", ->
+        it "does not create folds in the other display buffer", ->
+          otherDisplayBuffer = new DisplayBuffer(buffer, { tabLength })
+          displayBuffer.createFold(2, 4)
+          expect(otherDisplayBuffer.foldsStartingAtBufferRow(2).length).toBe 0
+
     describe "when the buffer changes", ->
       [fold1, fold2] = []
       beforeEach ->

src/app/display-buffer.coffee

@@ -104,8 +104,8 @@ class DisplayBuffer
   # Returns the new {Fold}.
   createFold: (startRow, endRow) ->
     foldMarker =
-      @buffer.findMarker({class: 'fold', startRow, endRow}) ?
-        @buffer.markRange([[startRow, 0], [endRow, Infinity]], class: 'fold')
+      @findFoldMarker({startRow, endRow}) ?
+        @buffer.markRange([[startRow, 0], [endRow, Infinity]], @foldMarkerAttributes())
     @foldForMarker(foldMarker)
 
   # Public: Removes any folds found that contain the given buffer row.
@@ -129,7 +129,7 @@ class DisplayBuffer
   #
   # Returns an {Array} of {Fold}s.
   foldsStartingAtBufferRow: (bufferRow) ->
-    for marker in @buffer.findMarkers(class: 'fold', startRow: bufferRow)
+    for marker in @findFoldMarkers(startRow: bufferRow)
       @foldForMarker(marker)
 
   # Public: Given a screen row, this returns the largest fold that starts there.
@@ -161,7 +161,7 @@ class DisplayBuffer
   #
   # Returns an {Array} of {Fold}s.
   foldsContainingBufferRow: (bufferRow) ->
-    for marker in @buffer.findMarkers(class: 'fold', containsRow: bufferRow)
+    for marker in @findFoldMarkers(containsRow: bufferRow)
       @foldForMarker(marker)
 
   # Public: Given a buffer range, this converts it into a screen range.
@@ -375,7 +375,7 @@ class DisplayBuffer
     @triggerChanged(event, false)
 
   handleMarkerCreated: (marker) =>
-    new Fold(this, marker) if marker.matchesAttributes(class: 'fold')
+    new Fold(this, marker) if marker.matchesAttributes(@foldMarkerAttributes())
     @trigger 'marker-created', @getMarker(marker.id)
 
   foldForMarker: (marker) ->
@@ -521,6 +521,15 @@ class DisplayBuffer
   # Internal #
   ###
 
+  findFoldMarker: (attributes) ->
+    @findFoldMarkers(attributes)[0]
+
+  findFoldMarkers: (attributes) ->
+    @buffer.findMarkers(@foldMarkerAttributes(attributes))
+
+  foldMarkerAttributes: (attributes={}) ->
+    _.extend(attributes, class: 'fold', displayBufferId: @id)
+
   pauseMarkerObservers: ->
     marker.pauseEvents() for marker in @getMarkers()