extend SS chain backwards:  three SS matched CA(i-1) of SS110:

 - SS31: matching CA peak was an i-1, not an i
 - SS96: preceding aatype was not a Valine, as required by the
   sequence and the assignment of SS110
 - SS135: correct i/i-1 peak type and preceding aatype
add new i-1 peak to match i peak of preceding spin system