Add Warning and comment about ignore rules that target an existing member but do not have it as a source
No longer ignore rules that target an existing member but do not have it as a source; instead this rule signal that the input should be ignored.
Issue an error/warning when the source field of a rule is not a list of "type name"
Revert "Issue an error/warning when the source field of a rule is not a list of "type name""

This reverts commit 141f534e4dfd5fd1ff0346716a7e9f0bd39fa8a1.
Redo: Issue an error/warning when the source field of a rule is not a list of "type name"

Only complain when the rule has a function/code and not when it is only
an 'attribute' rule.

Extend the information printed in case of rule problems:

WARNING: IO rule for class MyClass - type required when listing a rule's source: source="fTwo"
The following rule has been omited:
   read sourceClass="MyClass" targetClass="MyClass" source="fTwo" target="fTwo" code="{ fTwo = -1; newObj->reset1(); }";
Fixes for JIRA-5298

  o RooAbsOptTestStatistic

    - In initSlave() move reattachement of branch buffers from interval vars to pdfs vars
      _after_ data->checkValidBins() as the latter won't work anymore after the redirect.

  o RooAbsPdf

    - Support specification of multiple fit ranges createChi2(RooDataHist&,..) and
      thus implicitly in fitChi2To(RooDataHist&...).

  o RooAbsReal

    - Redirect call of createChi2 with TList of RooCmdArgs to createChi2 with
      explicit list of arguments instead of calling RooChi2Var ctor directly in both
      (so that only one of the two needs to overridden in derived class RooAbsPdf)
Fix handling of rules for unversioned classes.

Unversioned classes' default version number is technically -1,
so we need to properly account for this in TSchemaRule::TestVersion
so that the rule applies to the default unversioned schema when
the rule specifies version="[1-]"