Removed redrawing triggers after Dimension methods

* As discussed in #871
* This was originally introduced in 8a35ebb29c4f to make sample 14
  work but it seems to work fine without, might have been
  misjudgement on my part or I'm missing something now
* It should work because the REAL repositioning on the GUI only
  happens through #_position which the slot positioning code calls.
  left= etc. just set values that are considered by the positioning
  code they should not have an effect by themselves
Slight layout changes in redraw aspec to fit 80 chars
Merge pull request #900 from shoes/no-left=-redraws

 Removed redrawing triggers after Dimension methods 

* All real positioning happens through _position
* Changelog: improvement