Don't tokenize files that have more than 10000 lines

src/app/tokenized-buffer.coffee

@@ -62,8 +62,11 @@ class TokenizedBuffer
     @invalidateRow(0)
     @trigger "changed", { start: 0, end: lastRow, delta: 0 }
 
+  tooBigToTokenize: ->
+    @screenLines.length > 10000
+
   tokenizeInBackground: ->
-    return if not @visible or @pendingChunk
+    return if not @visible or @pendingChunk or @tooBigToTokenize()
     @pendingChunk = true
     _.defer =>
       @pendingChunk = false