Store relative buffer path instead of id

This allows the tokenized buffer to be deserialized during reopening
from the pane container.

Closes #744

spec/pane-container-spec.coffee

@@ -109,6 +109,15 @@ describe "PaneContainer", ->
         expect(container.reopenItem()).toBeFalsy()
         expect(pane1.activeItem).toEqual item3
 
+      describe "when the last-closed pane item is an edit session", ->
+        it "reopens the edit session (regression)", ->
+          editSession = project.open('sample.js')
+          pane3.showItem(editSession)
+          pane3.destroyItem(editSession)
+          expect(container.reopenItem()).toBeTruthy()
+          expect(pane3.activeItem.getPath()).toBe editSession.getPath()
+          expect(container.reopenItem()).toBeFalsy()
+
     describe "when there is no active pane", ->
       it "attaches a new pane with the reconstructed last pane item and focuses it", ->
         container.attachToDom()

src/tokenized-buffer.coffee

@@ -27,12 +27,12 @@ class TokenizedBuffer
   constructor: (optionsOrState) ->
     if optionsOrState instanceof telepath.Document
       @state = optionsOrState
-      @buffer = project.bufferForId(optionsOrState.get('bufferId'))
+      @buffer = project.bufferForPath(optionsOrState.get('bufferPath'))
     else
       { @buffer, tabLength } = optionsOrState
       @state = site.createDocument
         deserializer: @constructor.name
-        bufferId: @buffer.id
+        bufferPath: @buffer.getRelativePath()
         tabLength: tabLength ? 2
 
     @subscribe syntax, 'grammar-added grammar-updated', (grammar) =>
@@ -44,6 +44,7 @@ class TokenizedBuffer
 
     @on 'grammar-changed grammar-updated', => @resetTokenizedLines()
     @subscribe @buffer, "changed", (e) => @handleBufferChange(e)
+    @subscribe @buffer, "path-changed", => @state.set('bufferPath', @buffer.getRelativePath())
 
     @reloadGrammar()