Fix to makeSepIndentPreSafe: always safe when nested in an indentPre!

* echo " ''a''\n  ''b''" | node parse --wt2wt was normalizing
  whitespace on the second line because makeSepIndentPreSafe was
  not checking if the separator came from a node that was nested
  inside an indentPre. A simple check for state.inIndentPre fixes
  this issue.

* Added a parser test to capture this which passes wt2wt mode.

* This eliminates dirty diffs seen in RT testing
  Ex: jawiki:ベルマン-フォード法

* Additional change: separator constraints were being destructively
  updated in --trace wts mode. Fixed this to prevent hair-tearing
  during debugging.

Change-Id: I2cc2e79137637df191c2544982cc08b2a0777de4
Merge "Fix to makeSepIndentPreSafe: always safe when nested in an indentPre!"