Make EditSession.copy return a copy with a unique id and markers

We want to be able to use the copy independently, which means we
should not use EditSession@deserialize to create it because that will
tie us to the same selection markers.

spec/app/edit-session-spec.coffee

@@ -15,6 +15,18 @@ describe "EditSession", ->
     buffer = editSession.buffer
     lineLengths = buffer.getLines().map (line) -> line.length
 
+  describe ".copy()", ->
+    it "returns a different edit session with the same initial state", ->
+      editSession.setSelectedBufferRange([[1, 2], [3, 4]])
+      editSession.addSelectionForBufferRange([[5, 6], [7, 8]], isReversed: true)
+      editSession2 = editSession.copy()
+      expect(editSession2.id).not.toBe editSession.id
+      expect(editSession2.getSelectedBufferRanges()).toEqual editSession.getSelectedBufferRanges()
+      expect(editSession2.getSelection(1).isReversed()).toBeTruthy()
+
+      editSession2.getSelection().setBufferRange([[2, 1], [4, 3]])
+      expect(editSession2.getSelectedBufferRanges()).not.toEqual editSession.getSelectedBufferRanges()
+
   describe "title", ->
     describe ".getTitle()", ->
       it "uses the basename of the buffer's path as its title, or 'untitled' if the path is undefined", ->

src/app/edit-session.coffee

@@ -117,9 +117,18 @@ class EditSession
 
   getState: -> @serialize()
 
-  # Creates a copy of the current {EditSession}.Returns an identical `EditSession`.
+  # Creates an {EditSession} with the same initial state
   copy: ->
-    EditSession.deserialize(@serialize())
+    tabLength = @getTabLength()
+    copy = new EditSession({@buffer, tabLength, @softTabs, @softWrap})
+    copy.setScrollTop(@getScrollTop())
+    copy.setScrollLeft(@getScrollLeft())
+    for selection, i in @getSelections()
+      if i is 0
+        copy.setSelectedBufferRange(selection.getBufferRange(), isReversed: selection.isReversed())
+      else
+        copy.addSelectionForBufferRange(selection.getBufferRange(), isReversed: selection.isReversed())
+    copy
 
   ### Public ###