Bug fix in AttributeExpander introduced by git SHA 46119efb

* AttributeExpander stopped cloning tokens always -- it started
  cloning them on demand to eliminate useless work/memory use.

  However, this broke RTing of certain pages in 'roundtrip-test.js'
  (not when run via node server for some reason) because the KV
  obj. of original token was being modified via newAttrs object.

  This is because AttributeTransformManager was reusing the original
  KV object from the token's attributes when its k and v properties
  were strings (the common case).  But, in that scenario, there is
  no ksrc and vsrc to be updated either.  So, the fix is to not
  bother updating ksrc and vsrc in newAttrs[i] in AttributeExpander
  if they dont exist.

* Verified by testing with "node roundtrip-test.js Yelena_Romanova"

* No change in parser test results.

Change-Id: I54c53ae4f380532048a59240a03f9e4a7c867d1b