Fix regression in tokenizer

 * Introduced in 2dad972c78134de0270152d1e10a96cb2a294eae.

 * When a matched expression has consumed tokens and we explicitly
   abort, be sure to backtrack to the reported position.

 * Cleans up the large diff when round tripping
   cawiki/2011_en_els_vols_espacials.

Change-Id: Icb0dd6ca5d2c49f6e4543c5dc4bafb863903bf3a