Prepare cling for fixing bug #98146. In principle the bug could be fixed in 10

seconds, but I don't like where EvaluateInternal is going.
At first place it shouldn't do any smart guessing what the transformers would do.
Second it shouldn't try to attach expression evaluation (storing the result in 
cling::Value) while preparing for value printing.

To sum up:
* Simplify the old craft in EvaluateInternal
  - Move the value printing logic into the value printer transformer. 
  - Move the expression evaluation login (mainly coming through the 
Interpreter::evaluate interface) into separate transformer.
* Attach the new transformer to the list of transformers (the size of it was 
increased as well.)
* Add new compilation option switch that the new transformer will react on.
* Turn on the switch where necessary.
* Simplify value printer logic. Now everything is at one place, which makes it
simpler and easier to debug.
* Make IncrementalParser::Parse to take compilation options' reference instead of
constructing it's own.
* As consequence of the new implementation - two bugs in the testsuite were 
uncovered. Propose a fix for them.
* Improve documentation.
* TODO: There is some code duplication, which will be factored out soon.


git-svn-id: http://root.cern.ch/svn/root/trunk@46549 27541ba8-7e3a-0410-8455-c3a389f83636