use constructor to initialize hash or array variables, postscript to do widget lifecycle stuff

[bill]

1. in Widget.js, call create() from postscript() rather than constructor():

       postscript: function(params, srcNodeRef){
           // this happens only after all construction is done
           this.create(params, srcNodeRef);
       },
   

2. certain widgets have code in preamble(). move that to constructor() instead.

3. ValidationTextBox? and Combobox have code like

   if(this.query==dijit.form.ComboBoxMixin.prototype.query){this.query={};}
   

to make sure that each widget gets it's own copy of query (but that we don't overwrite a parameter specified to the widget constructor (and mixed in to the widget). Should be changed to simpler

constructor: function(){
  this.query={};
}

[bill]

See [10190] for example.

[bill]

Scott says we should stop using preamble because it will break if it's called from a mixin (meaning, it will execute too late for our purposes). Changing bug description for new approach.

[bill]

(In [10412]) 1. in Widget.js, call create() from postscript() rather than constructor()

2. for widgets using preamble(), move code in preamble() to constructor() instead.
3. change ValidationTextBox? and Combobox to use constructor to initialize arrays/hashes, rather than if() statement referencing prototype

Fixes #4076.